The following is the Collectors' Clearinghouse column from the Jan.
23, 2017, issue of Coin World:
An overdate occurs when a date (or part of a date) is punched into a
finished working die that already has an older date (usually that of
the previous year). Kevin Flynn (in a personal communication)
estimates that there are around 200 domestic overdates, most dating
from before 1850. In many cases, overdates appear to represent
expedient measures taken to address a shortage of dies or to avoid the
labor required to fabricate new dies.
Overdates must be distinguished from Class III doubled dies, an
unrelated die variety that can also generate overlapping, mismatched dates.
Among domestic coins, the conditions necessary for the production of
overdates ended in 1909, when the final Indian Head cents were struck.
This was the last issue in which the date was punched into each
working die by hand.
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After that, the date was incorporated into the master hub or the
master die. Mismatched, overlapping dates later than 1909 represent
Class III doubled dies. One of the best-known examples is the 1942/1941 Winged Liberty Head dime.
Winged Liberty Head
dime: The Winged Liberty Head dime – popularly though
erroneously known as the "Mercury dime" for Liberty's
resemblance to the fleet-footed Roman messenger god – is considered
by many the most attractive U.S. 10-cent coin. How
much are Winged Liberty Head dimes worth?
In various other countries, the practice of punching the date into
each working die continued into the late 20th century.
In many domestic overdates (especially the later ones), the earlier
date appears thinner and smaller than the later date. This pattern
also applies to foreign overdates, such as the 1925/1924 Switzerland
1-rappen coin and the 1900/1890 Peru half dinero shown here. The
attenuated older date could theoretically result from a light
application of each number punch (or multi-element logo punch). This
is because, in most punches, the working end of each raised number
defines a numeral that is smaller and thinner than the one defined by
its broader base.
That said, it’s difficult to come up with any scenario in which a
mint worker would choose to tap a shallow date into the die face. Most
traditional explanations instead see the attenuated under-date as
being caused by intentional abrasion of that area of the die face. As
one grinds away the metal surrounding the recessed date, you
eventually reach the level at which the numbers are at their smallest
and thinnest. After that, a new date can be punched in.
The problem with this explanation is that such a grinding
operation should create a depression in the die face that would show
up on the coin as a bulge. But no such elevation is ever seen.
A more extensive zone of abrasion would produce a larger, more
gradual, and less obvious rise in the field, but would also result in
loss and attenuation of adjacent design elements. This is also
something we don’t see.
So there must be another explanation. I sent an open-ended inquiry
to several die variety experts, and they presented several working
hypotheses that might solve this riddle. No single hypothesis is
applicable to all issues, nor would any one explanation necessarily
apply to all overdates within an issue.
The Cherrypickers’ Guide to Rare Die Varieties of United States
Coins (sixth edition) lists five strong-over-weak 1883/2 Shield 5-cent coin overdates. In
addressing these coins, Bernus Turner suggests that the entire face of
the working die was ground down to such an extent that only a trace of
the original date was left. The nearly-featureless die was then
annealed (heat-softened) and rehubbed with the Shield design. After
that the later date was punched in over the earlier one. He further
suggests that the abraded die face was left slightly convex in order
to make hubbing easier and avoid radial bulging of the die neck. In
his opinion, these efforts were primarily undertaken to salvage worn,
damaged, and slightly cracked working dies.
Since none of the Shield 5-cent coin overdates are associated with a
doubled die, this implies that the working hub was placed perfectly
over the remnants of the original design during the later hubbing.
Kevin Flynn analyzed the four strong-over-weak overdates known for
the Seated Liberty half dime (The Authoritative
Reference on Liberty Seated Half Dimes, 2014). These overdates
are restricted to the years 1848 and 1849, and in every case the final
digit was punched over a 6. Flynn believes that, in each case, an
1846-dated working die was ground down (leaving a remnant of the 6)
and then rehubbed with the same design (sans date). The later date was
then punched in by hand.
More than 25 strong-over-weak 1880/1879 overdates are known for the Morgan
dollar, with the Philadelphia Mint and all three other Mint facilities
represented. In his recent reference book, The Top Morgan Dollar
Die Varieties (2015): Flynn asks, “Was the original date only
struck lightly into the working die? Did die steel displaced from the
new date being punched into the working die get pushed into the
incused space of the original digit? Was the face of the working die
ground down to remove the remnants of the digit? Was the incused space
of the original digits filled with die steel? Was the metal
surrounding the original digit heated in a manner to force it to flow
into the incused space of the original digit?”
For decades the Morgan dollar has ranked at the top U.S. coin
collectors' favorite coins. Why is the Morgan dollar so popular?
There are many reasons, including: large size, attractive designs,
numerous varieties, historical significance. How much are
Morgan dollars worth?
After an exhaustive analysis, Flynn rejects all these scenarios and
concludes that the vast majority of these overdates are actually Class
III doubled dies. He argues that an incomplete first hubbing with an
1879-dated working hub (one that left the peripheral details like the
date weak and incomplete) was finished up with a final hubbing using
an 1880-dated working hub.