After all, our development consoles (which the PC debugger connected to) worked just as well on a cartridge from the store as on the code we uploaded to it. So if you were impressed by an effect in a game like Ranger-X, you just plugged it in and explored it in the debugger for a while. You'd end up with a new technique and (quite possibly) a snippet of code you could try out on your project. Happened all the time.
Now, I don't think anyone really undertook an effort such as this to lovingly decompile a game with comments on this level, but there were decompilers too. I was always suspicious that our studio's highly sophisticated platformer engine was based on lots of, uh, best practices. If you know what I mean. But that wasn't a big deal.
It's interesting because when I later heard about the tech behind the Halo engine, I realized I'd never seen their architecture before — because things had moved on and gentlemen of game development didn't decompile each other's games. They licensed their engines instead. If this had been the cartridge age, lots of people would have totally lifted their approach.
By the way, the talk I heard, a detailed overview of how the Halo 2 engine works, is available at the page below. Yeah, it's from seven years ago but it was a ten-year-old engine already. Good code design lasts. If you like game guts, this page is a little-known treasure.