Somehow, somewhere people started referring to hardtops as coupes. Maybe because hardtops are not sedans? (more on this in a bit) This opened the door for the 'post coupe' term. Needed to have someway to discern between coupe (actually a hardtop) and a post coupe.

A hardtop does not have a 'B' pillar between the door glass and quarter glass and as stated previously, all side glass (less vent wing) roll down. Body designation 23. Sometimes referred to as a coupe (like the YO info) but that is wrong. No offense to anyone that doesn't know any different.

A coupe has the same roofline as a hardtop with the addition of the 'B' pillar between the door glass and the pop out quarter glass. Body code 21. (for 68-70. pre 1968, 21 is a sedan.) Also called 'post coupe'. To alleviate confusion, the term post coupe is a redundancy.

A sedan has the frames around the windows, a 'B' pillar and a different roofline than a coupe/hardtop. Compare the roofline from a 68-70 sat/belv. 4 door vs. a roadrunner or gtx.

Hope this helps.