As I found out the hard way, the Gottlieb DMDs all roll at 10 bil--and don't save that fact. Womp womp, no high score for you.
Quoted from mbaumle:
Actually, the number 2,147,483,647 is the highest possible number for a 32-bit binary integer. I'm guessing that 4 billion was just an arbitrary number that was chosen during programming.
Scores are unsigned integers, which gets you another factor of two.