Never heard about a TAS-limitation. Only either IAS (Vmo) or M (Mmo).
I don't believe anybody said anything about a TAS limitation. Limitations are described in CAS in some aircraft, however.
I frankly donīt know how my aircraft behaves beyond Vmo/Mmo, but Iīm not too curious to find out about it either. Maybe thereīs no buffet or the like, but I donīt care if I overstress the structure with a slight elevator movement
The aircraft isn't going to be overstressed by flight up to Vmo/Mmo. Nor are you going to see adverse flight characteristics at that point. A manufacturer isn't putting a limitation at a point beyond which flight characteristics decay or the aircraft is unsafe.
Structural damage can be done at speeds far below Vmo; structural damage can be done, and has been done, below maneuvering speed. A good example of that was the loss of the Airbus A300 vertical stabilizer on American Airlines Flight 587, out of JFK, in November 2001.
You can break your airplane at low speeds, too.