not 100% correct.
Back in the day, no artglass signature was applied until the very final stage. The real artglass was even noted where it was sold.
This was done in the art glass department which did exist pretty much until the end.
During the 80's there was only one person who did that(a woman). Before that a man, not sure how long he did it.
Standard production pieces in some cases was signed already in the production( I have done it myself).
When you see a artist signature that is hand written on a limited art glass piece, this is actually done by the artist. But just the signature, nothing else. Engraved pieces never have this type of signature.