Hey, if I see a member of a system using first person plural a lot, should I refer to them in second person plural or just second person singular? (I'm Texan, I'm allowed to y'all.)
You... should refer to them with second person, silly.
We always refer to who we're talking to singularly. If we want to say something about their system specifically, we will say "your system" (or "your collective" / etc as preferred) or just "you all" (without the contraction).
No matter what type of switching they use, or how blurry or blended or fused they are at the moment, "you" nearly always works for referring to whoever you're speaking to, and is always a good default.
For referring to the entire system there are ways of communicating that, too. Sometimes it is indeed just a collective "you" if you're speaking to someone or something (psst @Kamagami) without second-person (such as using it/its in place of singular "you").
Hi there!
But yea, it can attest to this: pretty good guidelines to follow. If you're ever too unsure: try asking! It may be a little daunting, but a lot of the time people are fairly open to being asked, especially if you do your best to respect their preferences