There was a discussion on this before. No where it is written that BUSS is only reliable or usable below 250 due to Mach effect etc. It is all guess work. The FCTM says:
The BUSS enables to fly the aircraft in the entire flight domain while observing the design limits.
If stall warning is valid above 250 which also comes from AOA then BUSS display should be valid. All that airbus says about above and below 250 is what I said before. However the irreversibility part was quoted by some one in FCTM but I couldn't find it.
Code:
How so? Why couldn't you switch one (all) back on if the crew turned them off in error or when out of the condition which caused the UAS in the first place?
If you switched off all ADRs there is no way of knowing that UAS has disappeared.