@aeva @oblomov having once worked (in ~2012) on a "rational reconstruction" project for a 25+-year-old software system where the source code might have been available (on magnetic tape in someone's garage, perhaps), we didn't bother to try to dig it up, because even if we had gotten the tapes, getting the equipment to read them and then trying to assemble an emulation environment for decades-old LISP seemed not worth it.
We worked from the 700-page dissertation instead, but there were indeed many things that were vague enough we didn't feel confident in what the original had done. Source code probably would have helped us a fair bit even if we couldn't run it, but I can't imagine a process by which a runnable version could have survived all the tech changes of the intervening years.
There are game preservationists doing really interesting projects (https://dl.acm.org/doi/abs/10.1145/3102071.3102092 is an example and this site which seems semi-defunct has an example: https://gisst.dev/). ROM-based games are indeed much easier to preserve. I crossed paths in grad school with someone who wrote about Adobe Flash as a platform, and I'm sure many of those games are essentially lost to inadequate emulation fidelity.