70 and first 71 half shared same frame and back panels with hinge covers and big release button. Second 71 half year shares same 72/74 frame and packing panel, with one piece panel and small release button.
Foams and covers are the same between 70 and 71 ( both halfs ) but not the same with 72/74s
So if you try to fit 70/71 on to a 72 and later will need to change the foam too... DUNNO if is the earlier kind with big release button the trimmed area around release button will mean some problem on a 72 and later ( second 71 half included ). I think not since it should be covered by the later back panel without problem.
If the seat is later 71, then is a "headache" less to get worried about the trimmed area.