but there's no evidence that it's the case for electric trim.
Agreed. There is the suggestion though, that the pilots, after the again assumed switching back on, of the electrical trim... Only apply relatively short trim up commands... as perhaps the TRIM appears to be jammed to the pilots. The FDR doesn't seem to show any significant movement in TRIM to their last commands. The subsequent MCAS TRIM down, seems to have an immediate effect.