Originally Posted by Mrs Vimes
Going back to your old cast after you've brought in the new faces is also, in a way, "living in the past".
XOW was set after First Class and if he appeared in X4, he would only been 10 to 15 years older.
And going back to the original cast is not "living in the past" simply because their timeline is set in the present not in the 60s.
Original trilogy = present timeline
First Class = past timeline