The following is the Collectors' Clearinghouse column from the March 28, 2016, issue of Coin World:
Off-metal errors enjoy enduring popularity among error collectors. The most sought-after type is the transitional planchet error. These off-metal errors involve a coin being struck on a planchet whose composition matches that of an earlier or later year. The most famous examples are the less than two dozen 1943 Lincoln cents struck on bronze planchets, instead of the zinc-coated steel planchets designated for that year.
Transitional planchet errors most often occur when an obsolete planchet is left behind in a hopper, conveyor, or tote bin during a changeover in composition. The laggard planchet is then buried under a mountain of date-appropriate planchets.
A planchet that matches a later year is a bit harder to explain. This most often occurs when there is some overlap in the production of the two successive dates and compositions. It’s not uncommon for a mint to get a head start on the next year’s production by starting the presses during the tail end of the preceding year.
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Circumstances surrounding the appearance of transitional planchet errors are not always the same. The ideal circumstance involves two different dates with nonoverlapping production schedules. The absence of 1942 steel cents is consistent with a break between the production of bronze and steel cents.
Production overlap may explain the several 1999 Anthony dollars struck on manganese-brass clad planchets intended for 2000 Sacagawea dollars. Sacagawea dollars were struck as early as Nov. 18, 1999, providing some opportunity for a “golden” planchet to migrate to presses still striking Anthony dollars. Conventional explanations involving leftover planchets can account for the complementary population of 2000 Sacagawea dollars struck on obsolete copper-nickel clad Anthony dollar planchets.
A number of 1944 Lincoln zinc-coated steel cents are known from all three Mints. These were struck on steel planchets identical to those used the previous year. But there’s a complicating factor, at least when considering those produced at the Philadelphia Mint. In 1944, the Philadelphia Mint struck 25 million Belgium 2-franc coins on leftover steel cent planchets. As a result, any 1944 steel cent struck at the Philadelphia Mint is just as likely to be a foreign planchet error as a transitional planchet error.
A respectable number of transitional planchet errors are associated with the switch from silver-alloy to copper-nickel clad planchets. The last authorized date for circulation-quality coins struck on silver planchets (dimes and higher denominations) is 1964. Therefore, any coin dated 1965 or later that is struck on a silver planchet is considered to be a transitional planchet error, as is any copper-nickel clad coin bearing the date 1964. The chances that such errors would occur increased significantly as the Mint continued to strike 1964-dated silver coins through March 1966.