No Mintmark Rare Proof Sets

The question had crossed my mind a couple of times as to why the SF Mint would leave the MM off the coins of their own production.

Perhaps the dies for these no MM coins were sent from Philadelphia, and someone forgot to put the MM on the dies.

And how could a person not see it was missing a mintmark when they put the dies on the machine? He must have been blind or it was done intentional, since proofs are shown extra care, or at least they are supposed to.

In a way I'm glad there are proof errors, since I do like them. I just don't have or found any, yet.

I don't even know if that is possible to cherrypick something like that, since it is so obvious. When I buy sets, the dealers always look them over, so for me, it wouldn't be possible.

The dies were stored for destruction at the end of the year. When the error was discovered they went back through the dies and found the one with the missing S. Then they checked the record of its use which lists the number of strikes it was used for.

For die errors they are more likely to have an idea of mintages than they would of striking errors, and most "sexy" errors are striking errors. And for die errors they have to be discovered during the year of issue else the dies are gone. Also doe to the sheer number of dies used, it would not surprise me if they did some die destruction from time to time during the year to gain room. Especially for the cent dies. This would shorten the amount of time in which the error would need to be discovered.