Quoted from vireland:
Dunno. I've seen the most horrendous code management and deployment processes at so many major game software companies firsthand over 25 years that I am extremely jaded about that kind of stuff. There's the right way and then there's the way it usually gets done. Given the two clear markers (Kiss Army Multiball appearing in AS menu, and the AS song bug that behaves exactly like the KISS one) I'm pretty sure best practices were not in force for at least part of the project.
Code was in fact terrible 25, 15, even 10 years ago. Not all of course there are always exceptions
But generally modern techniques and methodologies for developing software in a responsible manner have only really become more mainstream over the last 10 years or so, maybe only reaching wide adoption in the last 5. Unfortunately there are still way too many out there not yet leveraging these techniques.
My guess is that with stern moving to modular hardware they would have also taken it as an opportunity to properly abstract and modularize their code base... at least I sure as hell hope so.