Had the same problem , twice. Two different cars, two different body shops (both friends), 20 years in between. Both times the work was excellent. Still friends with both guys. As someone stated above, they don't make a whole lot of money on these cars, so they do other things in between that they do make a lot on money on. It is hard to be understanding when it is your baby that you are waiting for but most times it pays off in the long run.
I did have another car painted between the two that I listed above and that one moved along quickly,(same guy that did car #1)
With that one we traded labor, I did remodeling on the office of his shop and he did the body work on my car. I was there a lot of days working for him and he did a lot for me. The car was in and out in about 2 months. That was in '95 and the paint still looks pretty good considering that the car gets driven quite a lot.