Or would the AP have been dialling in more trim before this point, and *that* ought to have been the clue?
Yes-it would have to trim almost continuously once the speed decayed below Vref-but there were probably a lot of other distractions starting to creep in by then.
Cargun- according to Safta's experience in the -300 Sim, it isn't altitude related, but trim ie there will be a critical combination of NU trim and low airspeed from which a successful recovery is unlikely, if not impossible-particularly if the TL's close again and the recovery isn't 'by the book'
I imagine that with a well co-ordinated, pre-warned crew, both assisting on Flt Controls/TL's, and continuously trimming, there will be a recoverable IAS/Trim/Altitude-but impossible to predict without running in the Sim, and even that model may be inaccurate as you are well outside the design parameters (as per the jet upset model which is marginal at best)