A coin struck on dies from two different countries is extremely rare, especially when itís on the same denomination, involves a U.S. struck coin, and has 2 different dates.
This recent discovery is a major mint error involving Mints from the U.S. and Canada. Itís a 1973 U.S. Cent that was overstruck by 1978 Canadian Cent Dies! Lincolnís portrait and the date 1973 is clearly visible on the obverse, and the Lincoln Memorial is very visible on the reverse.
There are a few known U.S. coins struck on Canadian blank planchets, and a few known Canadian coins struck on U.S. blank planchets, but this is the only known Canadian coin of any denomination that was struck on a previously struck U.S. coin.
Itís also a dual-date which adds to its excitement and rarity.