Hmm, i suppose so, but maybe they have started from the ground up on a simple kind of power armor, after examing captured Brotherhood suits, or maybe even Enclave power armor. I mean the Enclave had a way of making Power Armor, and the NCR coul've copied/caputered the things that make it?
Even if they try to copy it they don't have the right resources to make an exact copy of it.
At most they could very probably create a replica, but it wouldn't be able to use that fusion stuff it has and... To simplify: real power armor gives + in strength, a replica would give - in strength.
So sure, they
could copy it, but it would be far inferior to the real deal.
Greatest AliveYes, they did, but we have no idea how big the Enclave really is/were. We have no idea how many bunkers of just different materials they have. But I believe they don't know how to produce more materials, so once they've looted all their structures they'd be empty handed.
Oh and Enclave were part of united states government, I'm sure they had the blueprints for power armor.