+1almarg. No reason to doubt the person. What's interesting to me is to understand how the evaluation process was done. To know the amp was changing after that much time, it would also be necessary to know that nothing else in the complex system (cables, etc.) is changing and yet being attributed to the object of analysis. (I assume the other components are all stable, i.e., "burned in"?). And the room and other contributing environmental conditions (including power) are being controlled, too? Then there's the question of memory and linguistic description. Are notes being kept? Are the terms used in the notes precise? Etc.
What makes these kinds of issues tricky for me is that there is the sound of a precise, scientific approach, but there's either an irregular process or one that is not carefully documented. I've got nothing against shootin' the sh*t, but when it sounds like it's something else, I lose interest.
What makes these kinds of issues tricky for me is that there is the sound of a precise, scientific approach, but there's either an irregular process or one that is not carefully documented. I've got nothing against shootin' the sh*t, but when it sounds like it's something else, I lose interest.