I once bought four NOS Bally SS glasses from a guy, and none had CREDIT on them.
I think the rule is that original backglasses do not have silkscreened letters. If CREDIT is there, it's a sticker. But I could be wrong.
My repro Fathom has CREDIT silkscreened on.
I've seen the CREDIT sticker applied slightly crooked. Not an uncommon sight.