I think I have read all the contributions. There is no mention of coffin corner in the thread.
Does the AB 330 not have such a problem? Could someone with practical knowledge of the aircraft estimate whether at the assumed weight and altitude what margins there would be at the cruising altitude. Also would the climb to FL380 have put them into coffin corner? Once there of course (if it exists for the AB) the aircraft would be buffeting with an increase or decrease of speed (Mach No.)