I know about the identity protection PIN, so I've been assuming this whole time that's what I was choosing a number for. It is possible I was just doing the self selected PIN and wasn't aware that I should be doing something additional for other one. FWIW I haven't needed the PIN later but saved them in case I did.
Does it serve a security function? Am I supposed to remember what it is?
I know the IRS does have an identity protection PIN process, but that's separate.