I've heard that this can happen when a car is improperly jacked up. Because these cars have so much flex to them, if you jack one corner up very high, and 'twist' the car, you can damage your t-tops. On a flat lift hoist, I see no problems...
Some people keep the t-tops latched and windows rolled up, others roll down the windows and loosen the t-tops, while still others remove the t-tops entirely before lifting.
My car has never suffered damage, but I don't have glass t-tops. Maybe someone else here will have correct information.
My 77 also has the G.M. cancelled CC1 Moonroofs option. I never made a fuss about the removel or the unlatching of the tops during jacking or raising the vehicle. However, I recently had the tops restored; repainting, glass polishing and new weatherstrips. With the new weatherstrips I had to change the shims on the pins for proper fit and this seemed to tighten the top up a bit. So, in the future I will unlatch the tops just to play it safe. If the glass would happen to crack it leaves the top useless as no repairs to the glass can be made and replacement of the glass is impossible due to the curve and shape of said glass. NOS glass would have to found to make the repair and I have never seen a listing for NOS glass for the Moonroofs. I have seen NOS unpainted Moonroofs listed in the past but the price was very high.