[vintagecpa]

I was researching the 1958 master set. Obviously, the Herrera error card is one of the key cards. My question is why is this card considered an error card and needed as part of the master set? In the examples I have seen, the "a" isn't missing, but only partially missing because of a quality control issue with the printing. I just don't see the big deal with this card. If every card with these type of issues was considered an error card, it would be impossible for any master set to ever be completed. Any thoughts?