Coin Variety Identification: RPMs, OMMs, Doubled Dies, and Overdates

"Die variety" is the umbrella term that covers at least a dozen distinct things — and knowing which specific type you have is the difference between a common coin worth face value and a documented rarity worth hundreds or thousands of dollars. A doubled date, a strange mintmark, and a digit visible in an unexpected place all look like "something odd," but each is created differently, catalogued separately, and valued independently.

This guide defines the six variety types every collector should recognize, explains how to tell them apart from worthless machine doubling and damage, and walks through the practical steps for identifying and attributing what you have. A good loupe or microscope is your primary tool throughout.

The six variety types every collector should recognize

Each type below has a distinct origin. Confusing them — particularly conflating doubled dies with machine doubling — is the most common and most expensive mistake newer collectors make.

1. Doubled Die (DDO / DDR)

A doubled die is created during the die-making process, not during striking. The working die is hubbed (pressed against a master hub to transfer the design) multiple times. If the die shifts slightly between hubbings, the resulting die carries a doubled image permanently baked into the steel. Every coin struck from that die shows the same doubling in the same location — it is a die characteristic, not a planchet or press accident.

DDO means the doubling is on the obverse die; DDR means it is on the reverse die. The most famous example is the 1955 Doubled Die Obverse Lincoln cent, where the date and lettering show dramatic separation visible to the naked eye. The 1969-S Doubled Die Obverse and the 1972 Doubled Die Obverse are two other high-value examples. Our 1955 Doubled Die guide covers what to look for in detail.

Key diagnostic: doubling on a true doubled die is rounded and shelf-like, with the secondary image showing full design detail. The doubling appears identical on every coin from that die.

2. RPM — Repunched Mintmark

Before the Mint switched to hubbing mintmarks directly into working dies (a change phased in starting with cents and nickels in 1990 and the remaining denominations in 1991), mintmarks were punched into each die individually by hand. If the punch was applied more than once at a slightly different angle or position, the die retained evidence of both impressions. The result is a coin showing a primary mintmark with one or more secondary mintmark images visible above, below, or to the side.

RPMs are among the most common collectible varieties in 20th-century US coinage. The Repunched Mintmark guide covers how to grade their severity (RPM-001, RPM-002, etc., in standard registry numbering) and which series produce the most valuable examples. Strong RPMs — where the secondary mintmark is dramatically offset — carry meaningful premiums over common dates.

3. OMM — Over-Mintmark

An Over-Mintmark is a specific subtype of repunching where the secondary impression is from a different mintmark letter than the primary one — for example, a D punched over an S, or an S punched over a D. OMMs occurred when a die prepared for one mint was redirected to another, with the original mintmark only partially obliterated before the new letter was punched over it.

The classic example is the 1938-D/S Buffalo Nickel (cataloged as FS-512 and related Cherrypickers' numbers), where the S mintmark is clearly visible beneath the D. OMMs are rarer than RPMs by definition — the logistical conditions that produced them (reassigned dies, mintmark changes mid-year) were less frequent — and they command larger premiums because the two-letter story is immediately visible and easy to explain to a buyer.

4. Overdate

An overdate occurs when one date (or a single digit of a date) is punched over a previously punched date on a die. This happened most frequently in the 18th and 19th centuries, when dies were expensive and reusing a partially prepared die by repunching the date was economical. The earlier date shows through wherever the new punching did not fully cover it.

The 1918/7-D Buffalo Nickel is one of the most prominent 20th-century overdates: the 7 from a 1917 date is clearly visible beneath the 8, and the coin is a major key date in the Buffalo Nickel series. See our Buffalo Nickel key dates guide for context on where overdates fit in that series.

Distinguishing an overdate from a doubled die on the date: an overdate shows two different digit forms (e.g., a 7 shape under an 8 shape), while a doubled die shows the same digit offset from itself.

5. Repunched Date (RPD)

A Repunched Date is the date equivalent of an RPM: the same date digits were punched into the die more than once, with slight misalignment between impressions. RPDs are most common in series from before the mid-20th century, when individual digit punches were used rather than a single logotype punch carrying the entire date. On an RPD, you may see a ghost of the same digit peeking above or below the primary impression — for example, a secondary "9" visible above the primary "9" in a four-digit date.

RPDs are catalogued in CONECA and Variety Vista listings. Mild RPDs carry modest premiums; dramatic examples on otherwise common dates can significantly exceed catalog value for the plain date.

6. Misplaced Date (MPD)

A Misplaced Date occurs when one or more digits from the date punch were accidentally impressed into the wrong area of the die — typically into the denticles, the field below the date, or even into design elements like the bust. The final date was then punched in its correct position, but the misplaced digit remained in the die. On the struck coin, a partial digit (or sometimes a nearly complete one) is visible somewhere it should not be.

MPDs are relatively uncommon and attract collector attention precisely because the misplaced element is so obviously wrong. Attribution usually requires a clear image of the misplaced digit and a cross-reference to the published variety listing for that date and mint.

Distinguishing genuine varieties from machine doubling and damage

The single most important skill in variety identification is learning to reject two impostors that flood online listings: machine doubling (also called strike doubling or mechanical doubling) and plain coin damage. Neither adds value. Both get misidentified constantly.

Machine doubling

Machine doubling happens at the moment of striking when the die or planchet shifts slightly during the squeeze. The result is a smeared, flat, shelf-like secondary image with no depth — the "doubled" element looks like it was wiped sideways rather than separately impressed. Under magnification, the shelves have sharp, squared-off edges and the metal appears displaced rather than raised. True doubled die doubling, by contrast, shows roundededges on the secondary element with full relief and design detail. Machine doubling adds zero premium; calling it a doubled die in a listing is a red flag for the seller's knowledge level.

Damage and post-mint alteration

A nick, gouge, or scratch near the mintmark area can superficially resemble a secondary mintmark impression. Die chips and die cracks are genuine die varieties but are not the same as RPMs or DDOs and are catalogued differently. Cleaning, artificial toning, and tooling can obscure or mimic variety characteristics. When in doubt, the question to ask is: does the anomaly show the same characteristics as a die-impressed design element, or does it look like metal that has been moved, removed, or added after striking?

How to identify which variety type you have

Work through this decision tree before pulling up any reference database:

• Doubling on the date digits only, no mintmark anomaly: start with DDO (if lettering is also doubled), RPD (if only the date is affected), MPD (if a digit appears in the wrong location), or overdate (if two different digit shapes are stacked).
• Anomaly on the mintmark only: compare primary and secondary impressions. Same letter, different position → RPM. Different letter visible beneath → OMM.
• Doubling on lettering, devices, or portrait: DDO (obverse) or DDR (reverse). Check whether the doubling is consistent with hub doubling (rounded, full relief) or machine doubling (flat, shelf-like).
• Digit visible in an unexpected area of the coin: MPD. Check denticles and the field immediately adjacent to the date area.

Once you have narrowed the type, photograph the coin under raking light with a macro lens or loupe-to-phone adapter and compare your image against the published variety listings.

Reference resources for attribution

Three databases cover the vast majority of US die varieties:

• CONECA (Combined Organizations of Numismatic Error Collectors of America) — maintains variety registries for doubled dies, RPMs, and OMMs across most US series. The CONECA numbering system (e.g., CONECA DDO-001) is the most widely cited in dealer listings and slab labels.
• Variety Vista — an online database covering Lincoln cents, Jefferson nickels, and other series in particular depth. Searchable by date, mint, and variety type with comparison images.
• Wexler's Doubled Dies— John Wexler's reference catalogs doubled dies with detailed class assignments (Class I through Class VIII, describing the geometry of the hub shift). The WDDO / WDDR numbering appears on many PCGS and NGC variety designations for Lincoln cents.

For Buffalo Nickels specifically, the Cherrypickers' Guide (Fivaz and Stanton) is the standard reference. The Buffalo Nickel key dates guide lists which varieties in that series carry the largest premiums and points to the relevant Cherrypickers designations.

When to send a coin for variety attribution

PCGS and NGC both offer variety attribution as part of their standard grading service for many series. A coin that receives a variety designation — for example, "1955 1C DDO FS-101" on the PCGS label — sells for a measurably higher price than the same coin in the same grade without the designation, because the attribution is third-party verified and immediately legible to buyers.

The practical threshold: if your variety, once attributed, would be worth more than the grading fee plus shipping by a meaningful margin, send it. For a dramatic doubled die on a major date, that math is almost always favorable. For a mild RPM on a common date where the premium is $15 over the plain date value, it usually is not. Research the published premium for your specific variety designation before committing to the cost.

Note that both services require the variety to be listed in their recognized references to receive a label designation. An unlisted variety — one you believe is new — can be submitted to CONECA for research before going to a grading service.

Variety collecting as a specialty

Many collectors build entire collections around a single series' varieties — every documented RPM for a given Lincoln cent year, or every known overdate in the Buffalo Nickel series. The 1937-D Three-Legged Buffalo Nickel is a reminder that die varieties are not always "extra" design elements — sometimes the variety is defined by what is missing, the result of over-polishing a die until a major design element disappears. That coin is now one of the most recognized varieties in American numismatics.

Whether you are cherry-picking individual varieties from dealer bins or systematically completing a variety set, the foundation is the same: understand the six types, know how to rule out machine doubling and damage, use the published references, and attribute before you price.