wow..>!
I am kinda baffled.:confused I have seen a top kinda stick before, but NEVER act like it was actually "stuck" in place...Usually its the exact opposite.
Having a "flex-frame" as some like to call it CAN work to your advantage. But re-mounting may be challenging. It is
POSSIBLE this car has been scratched and the "A" pillar might be tweaked out of shape a bit, binding the roof. Was the weatherstrip supposed to be new? Could they have been sloppy with the 3M adheasive? If so, it'll never come off...

That stuff is called "yellow peril" for a reason. Even if the front/top weatherstrip is damaged, its one of the easiest to replace...about $150 for that piece, but easy to do.
To see if the car was wrecked and might have some frame damage, look along the windshield for a pretty factory seal, and look carefully at the door edges for signs of repair. Look at the seams along all the body sections..they should be perfect. They sure are when GM rolls them off the line.
What you can try and its totally up to you, remove all the bolts, all 4,

then drive the car in/out of the driveway and turn the wheel as you roll up/down across the rise or dip at the edge of the street and your driveway. If that don;t pop the top off then its welded!
Just do NOT drive it far without the bolts....it'll fly off and behead the next guy,. and some
have flown off from the bolts being left out or the top simply breaking while the car was in flight.
Whats puzzeling is you WATCHED it being done, so its not some swindle the other guy is pulling...spilling a pepsi across the whole top trim is'nt enough to glue a top on that has the extreme physical stress that this car has on its roof.
Keep in mind the frame and the "A" pillar will twist when the car rolls onto a ramp and/or the steering wheels are turned to extremes. We fight this and we're willing (somewhat willing) to suffer harsh suspensions trying to prevent that natural effect of the C-4 frame.