The bubble level mounted next to the shooter lane on some games, was there a certain game they started including those on? Was it consistent where all games of a certain title and onwards got the level? Or was it like the way Diamond Plate playfields came to be, first with some titles getting a handful done like that, and then eventually they all got them after a certain point?

I have Williams Bally games from 1987 to 1995. None of my early games have that bubble level (Diner, Funhouse, etc.) but the Getaway does. And so does Theatre of Magic but World Cup Soccer does not. Thought maybe I might be missing one on a game that was supposed to have it, so figured I would ask here.