As a mentor who has done it dozens upon dozens of times, only about 10% of the time does anyone actually say when they are the new person.
PLEASE add a feature where we can see who is the new player in a trial or instance so we can at least explain certain mechanics to them. Otherwise it becomes a guessing game and it's just ... blah, inconvenient for all parties. It's fine when all 7 are new but when it's one that doesn't want to speak up, I really would just like to look at the party list and know who it is to explain mechanics to.