I can't believe I didn't venture to this part of the forum until I stumbled into another thread here...
I actually decided to complete the type set of the "World Coins Manufactured by Mints of the United States" since it's a bit more "manageable" at 387 coins. I have 275 graded with 81 raw coins that still need to be graded and 6 crossed over from NGC...
This is one tough set to find quality coins for. It's been years of searching to find the best quality coins that have not been cleaned or have issues. I have a stack of problem coins to prove it

Out of the 275 graded only 22 are in AU grades and further 6 below that with lowest being VF35. This set contains many conditional rarities and I don't mean just in MS grades. For many, it's tough to find coins that will straight grade...
If anyone cares, here's the link to my set:
https://www.pcgs.com/setregistry/alltimeset/383899AND to keep it on point with pictures... 1968 Canadian dime minted in the Philadelphia mint. Hard coin to track down in MS grade...

Philadelphia and Ottawa issues differ only in the number and shape of the grooves in the edge of the coins; the grooves have square bottoms on the Philadelphia coins and V-shaped bottoms on the Ottawa strikes." The story I heard is that Philadelphia used die collars from US dimes and that's the difference...