Plot hole: If Richard never reveals to Elise he is from the future, how then does the old Elise know where and when to find Richard to give the watch to and create a time loop?
Suggested correction: I agree this is not explicitly explained in the film. But because Elise was an actress, it's not a stretch to imagine that she would still follow the theater news, see the announcement of Richard's new hit play in 1972, recognize him, and go to the premier party to give him the watch.