737 Trim
Avoiding the closed threads, I'd like to enquire about the 737NG HS trim system. Evidence tends to suggest that in a specific and perhaps very niche corner of the flight envelope, due to powerful aerodynamic forces, the manual HS trim on at least one version of the 737 doesn't function as intended and, in all probability based on known facts at this time, the electric trim system can also becone overwhelmed in extreme circumstances. My question is: regardless of how unlikely it may be, how certain is it that other variants of the 737 can not end up in a flight regime, through some chain of undesirable events, whereby the trim system essentially becomes inoperable?
If it is certain this can't occur, how do we know with any certainty?