From 1971 to 1980 the Lombardo Mint in Canada minted these North Dakota Souvenir Dollars. There are 10 designs to this set. The 1971 has a more crude Indian design on the front than the rest and it can also be found struck in copper.
I have seen 1981 and later North Dakota Souvenir Dollars but they are made by Metal Arts Co. and in my opinion, not part of this set.
There might be a 1972 error issue or scarce variety, it may just be that of excess leftover copper planchets from 1971 used in striking some 1972 issues or perhaps some other minting error.
I'll look for others but not worried about them. There also may be an 11th "Special" edition in the mix.
I do like the Indian head on the front of these, which is what caught my eye to start, but I decided to make a set because I found 9 of the 10 in one lot at a really good price and then hunted down the 1973 to finish it up.