The root words in the examples below look fine even without a prefix:
un + bearable
ir + regular
dis + able
mis + fortune
… but not in these:
pro + gress
pro + mote
Possibly, I don't understand what a prefix really is. –pro in the above two examples may or may not be a prefix at all. But I would like to have these two points clarified.
1) Is it not always possible to separate a prefix from its root word because doing so will cause the root word lose all meaning?
2) Is it alright to look at –pro as a prefix in the above two cases because it's a prefix anyway and being detachable from its root word is not really a criteria for it to be a prefix?