The nut on the lateral shaft provides adjustment to remove the play to at least some extent. Some machines have a nyloc nut there and some don't. I change out to a nyloc nut if not originally fitted. Not sure how a plain nut was supposed to work in that location. Havnt noticed any other locking (staking etc.) on the plain nut machines.
Sounds like you have an engineering background so apologies if I'm stating the obvious.....
Cheers,
