Originally Posted by
FrequentSLF
however the information published does not validate a theory of the trace representing the thumb switch at the source
Or, more accurately, it neither validates nor invalidates the theory - we simply don't know.
But the fact remains that if it turns out that the FDR isn't showing the thumb switch position, then it contravenes the Annex 6 requirements.
Boeing have been building aeroplanes for long enough that one would hope they know what an FDR is supposed to record.