In any scientific endeavor, tests must be made with the fewest possible unforeseen variables.
With all due respect for your experience and diligence, (and we are impressed with both) every time you tell us more info, you make the detective work harder, rather than easier.
It is quite late in the game to admit that some of your test calls were from a cell phone. That in itself introduces a plethora of variables that can skew the results of your testing.
Telephone problems, while seemingly complex at first, can generally be reduced to a set of variables that is not unwieldy. As a wit on this forum often says, "It's all tip and ring."
We old farts do not consider a cell phone to be useful for anything resembling real telephony, especially when trying to test CO weirdness.
Sorry if I sound harsh, but we all have been there, done that, and we are sympathetic.
