> I’d wager 90% of working developers with a CS degree also could not pass a test in some random mathematical topic they studied X years ago in college either.

I wouldn't, either. But I've discovered that if I go about relearning it, it comes back very quickly. Having learned it before, I also recognize when I need to go relearn it, and what I need to know.

It's a lot better position to be in than having no idea how to go about figuring out how to solve the problem.