I reckon 90 percent of 1990,s DMD games don't have the last and updated version of the factory Roms.
It equates to gameplay wise, to buying a brand new Stern and never updating code.
Both home users and operators were too lazy to add the latest Roms or didn't know they existed.
Anyone and everyone should look on the Internet Pinball Database and see what the latest rom is for their pinball machine. It can make a big difference and it really does finish the code and adds so much to a game.
Check all your machines and see what Roms you have.
Im not sure that this is the case.
Some Roms have been updated or added to etc but that's not to say that a finished game didn't leave the factory... more that nerdy enthusiasts developed a game further years after its release because A: they can, and B: they like to show how clever they are.
You cant compare a Rom upgrade to A 90'S machine which was released as a full game and stayed that way for 15 - 20 years to Sterns release of half a game and continued upgrades as they finish it.