Are Demon and Dart seats different?

I Have A 72 Duster Rear Seats And 74 Dart Buckets I Ordered 74 Dart Seat Covers For Front And Back. I Assumed The Rears Would Be The Same. I Assumed Wrong They Were A Different Size. On The Back The Bottom Were The Same. So Yes They Could Very Well Be Different, Cause Mine Were. Hope This Answers Your Questions.