Re: Why the evolution of the term "prog"?
I would argue that the bands Foxhound listed above certainly had progressive elements in some of their songs from time to time ...but most of them imho are not what I think of as progressive rock bands and I have no doubt that those bands themselves would have said that to anyone who asked. Simply because rock itself evolved into various forms which carried along many bands doesn't mean those bands were attempting to be 'progressive' or trying to actually be prog rock artists. Bands like King Crimson, Yes, and Genesis on the other hand were imho attempting to truly make music outside the norm.
But as I said in another thread it's all subjective about who was trying to do what and why.