Don to Don:
As a scientist, you know that 100% certainty is rare. More often it's a probability approaching 100% (or not). Even when effectively something is treated as fact for all practical purposes, it may still not be 100% certain. Archaeology and history are especially subject to this, and a new discovery can invalidate years of carefully constructed theory. Ask the sextant-box experts about this.
Mostly we are dealing with probabilities and the preponderance of the evidence.
To get to 100% for the various Earhart theories requires a discovery that clinches the theory beyond a reasonable doubt.
For Crashed and Sank, find the airplane on the ocean floor far from Nikumaroro.
For Japanese Capture, find a Japanese government document from 1937 that clearly states this.
For Niku hypothesis, find the elusive "any idiot artifact" -- a part that could only be from NR16020 or human remains with identifiable DNA.
Even then, there will be skeptics who will insist that the evidence is faked. You can't convince everyone.
LTM,
Don