I can relate to this question. Four of the eight fish I have on the wall came from one taxidermist. Each time I had to wait about 14 months to get them back. The quality of the mount and paint job is phenomenal. That is why I kept going back.
One reason for his slow delivery times was that he did fish, game heads, waterfowl, turkeys, everything. He would get back logged from the deer heads and then try to play catch up during the summer.
He stopped running his own business because he wasn’t able to turn stuff over fast enough to make a good living. He can work for a “factory” taxidermist outfit and make more.
While the wait was always frustrating, I knew I would be happy when I got the fish. I have no idea if the guy you picked is in the same boat. Hopefully, you checked out his work before hand and got some references from people who had him do work. If not, do as someone else suggested; go to the shop and ask to see your fish. If it’s still frozen take it home and find a new taxidermist.