I'm usually wrong about most things, but I think maybe I know something you don't here. I believe a Gibson Thunderbird has a 9-laminate neck and a Classic-IV Pro has a 7-laminate neck. There may also be some minor differences in shape. I'm also pretty sure all of Gibson's bass runs are very low quantity, so I doubt that they spend more than a couple days a year cutting Thunderbird bodies. Given the low quantities and construction differences, I think it is fairly reasonable to believe that Gibson Thunderbirds are glued and cut in the United States.
Judging from the glue, sanding and finish work on my Gibson Thunderbird, I'm reasonably sure they only make Thunderbirds on Fridays after 3pm. Fortunately, they do fret work and set them up shortly after they hand out the bonus checks.