Jim wrote in message

One way to look at the "coffin corner" situation where some very
high-flying aircraft, such as the U-2, I suppose, can end up at an
altitude where the stall speed, in TAS, has come very close to the
Vne, as a TAS.

More precisely, I think it's when the stall speed (IAS in the cockpit)
but really a TAS issue) approaches the limiting Mach number. Since
Mach vs TAS decreases with altitude, and TAS vs IAS increases with
altitude, the problem is inevitable for the right (or wrong, depending
on your point of view!) kind of plane.

Kirk