I didn't realize they still had the fly window in 75, but I guess only the Valiant had it because Dusters had eliminated it on my 71 Duster and my 74 Duster. Another cost saving option at no charge.
Dusters/Demons/Dart Sports never had vent windows. The curvature on the glass prevented anything like that.
On the 2 door hardtop Darts the vent windows went away with the redesign in 1973. They stayed on the 4 doors (Darts and Valiants) because those doors were never redesigned. For example, all the other '73 up models went to plastic upper door panels. The 4 door uppers stayed metal, just like the '67-72 cars. The money savings was on the 4 doors, since there was no redesign, no new tooling, etc.
