I took the glass off and did some testing. Here's what I found with grandpa
1. If you start off the game like in the old code by shooting the two inside targets and then any of them, Grandpa will light but not be ready yet. You still have to get to 15 targets before enlarging ray is actually ready to go. This resets once munster madness is hit.
2. If you qualify grandpa via the chattering teeth while in a mode and shoot the scoop, enlarging ray will start. It's almost useless though as you can't see any of the lights for the grandpa mode. This goes for all modes and multiballs including munster madness.
3. If you start grandpa while in munster madness when you are done with munster madness grandpa will be complete for the next go of it. Since in multiballs a lot of targets are hit this is almost a guarantee to happen.
4. Chattering teeth appears to continue cycling between the playfield multi, bonus, and enlarging ray as you get farther in the game. It looks like you only get the extra ball once thru that mechanism
So it appears that there is some old code for grandpa still in there just not actually working. They might want to pause chattering teeth while in munster madness to reduce grandpa starting up there.
An idea for chattering teeth... Maybe after collecting the extra ball use that spot in the next level to relight mystery for MM 2 on.