"Cancel All Recurrences" works because it will keep already cancelled instances that way. When you reinstate the series, all the individually cancelled instances won't be un-cancelled, so "Reinstate All Instances" doesn't really cover it. It should be more like "Reinstate All Previously Un-cancelled Instances". How would we put that succinctly?

Alternatively, we can make reinstating a series un-cancel all cancelled instances. That would make some sense to me.

Technically I suppose you could have cancelled an instance after using "Cancel All Recurrences", which might make the word "previously" misleading -- "prior to now" is correct but "prior to the time when you cancelled all recurrences" might be the interpretation. So maybe "Reinstate All Currently Un-Cancelled Instances" is perhaps even more clear?

That wording seems perfect to me as-is. Clear as day.

Maybe it's fine to just use "Reinstate All Recurrences", and then explain what that means in the dialog? I suspect we aren't going to find a succinct, clear wording for "Reinstate All Currently Un-Cancelled Recurrences".

I just think it might not look pretty on standard resolutions (like my Mac)

Or the button could just say "Cancel All" and "Reinstate All" maybe? I think it's probably clear enough as long as it has different wording than the instance version, and has the word "all" or "entire" or "whole" or "series" or something on there: the dialog can clarify exactly what it means.

Yeah, I think the dialog should clarify.

(I don't like actually un-cancelling the instances because that makes cancel + reinstate not get you back to the original state, which is inconsistent with how those buttons work for other objects.)