both correct
the term "progressive" was being applied to many artists playing heavy electric music in the late 60s
the term "progressive Rock" began to be used in the early 70s and included many artists of all races and musical backgrounds from Jazz to Classical to R&B that often toured together as "progressive Rock" artists. It was definitely not a Brit-centric term.
the term "prog" appeared in the 80s seemingly to exalt only the British bands, practically expunging the contributions of all the great artists who were a huge part of the foundation of the whole scene in the late 60s-early 70s. It was commonplace in the 90s to hear Symph Weenies talk as if Genesis and Yes single-handedly created progressive Rock music and often point at earlier progressive artists as "not prog!"
as far as any 'return to glory', one should keep in mind that the songs that got heavy rotation back in the 70s were usually the weaker songs on their respective albums. Radio is and always has been a 'lowest common denominator' medium.
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