I've seen it as the credit lettering is just a sticker applied to the back of many bally glasses.

Same. Some of ours have a "credit" decal.

Same here on my NOS glasses, some have the decal and some do not.

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.

If its Centaur or Kiss, I think some early repros were made without the credit lettering. Most originals from Bally had the credit sticker, maybe not all.

I bought these from Royal Distributing,Cincinnati Ohio, early 80s. Started working there as a college work program. Went from ems to ss. Glad to have been able to see, play, and repair all those games from 80s-90s.

Just checked my games. Of 6 classic Ballys w/original glass 5 had the sticker. My Power Play was the only one w/o it. Most were slightly crooked on mine too. I've never removed one.

Bally might have made extras and never put the sticker on. My guess.

test it. Lay an original next to it. You will see if its an original.

Do you have the Kiss BG on Ebay for auction starting at $650? It does look good.

If that happened on one of today's new games, pinside would be up in arms and throw a fit!

Yes, I have NOS factory backglasses examples without decals in the credit area.
There are also examples where the word "credit" was ink screened versus a decal, but it depends on the age and title.
I am not speaking about any modern reproductions starting from around 1990.

This decal was normally installed after receipt of the backglasses from the screener, in preparation, but before actual game construction.

Many locations did not allow credits to be displayed due to gambling concerns. Hence the credit label was a sticker.

Also, did you notice the vanishing player-up lights? They were phased out to free up 4 bulbs for other features. There is a game or two that have the screening for player-up but the bulb was eliminated and replaced with a flashing score.