I'd add to also keep a copy of any substantial agreement/clarification alongside the proper legal paperwork. The PTO wording was a bit confusing, you ask for clarification and they tell you it's 21 work days and not 3 natural weeks? Keep a copy of those email/slack/etc., preferably one from HR and one from your manager where they both agree. Just push them in the same binder, they are probably not so many situations to make this bothersome but it can be helpful.

Luckily I've never needed it in any kind of legal situation, but a couple of times they saved me of a "he said she said" kinda conversation.