For chronological accuracy, I have been using the old name and gender when referring to a past, pre-transition person, and the new name and gender when referring to them generally.
But I had a realisation that this could be considered rude. I’d like to hear from some trans people on their opinion.
My friends have been really sweet and were referring to all past events with my new name, which I was initially surprised at. I think they are probably also trying to be careful to not offend. But yea if unsure, you can just ask.