A rate jam that causes a pogo to compress/extend will cause an extra 20lbs of control wheel force. The only tell-tale sign would be witnessing the failed PCU operating on the ground and seeing the pogo extend/compress.
But what (if any) visual clues would could one expect to see if the pogo(s) were stressed?
None, because the pogo was never stressed, it performed as designed and will return to its normal position with no damage when disconnected from the bad PCU.
My understanding is the input pogo(s) internal spring doesn't compress or extend until a pogo jam occurs. The bad/jammed pogo is back driven by the rest of the PCU assembly and it is then, that the spring, 'does its job'. So the pogos are usually quite rigid until a jam occurs.... is that correct?
Yes, except it isn't a pogo jam, it's a rate jam.
The only time I've had to change a pogo was due to external damage caused by rubbing against the metal safety loop attached to the PCU. That was on a single input PCU.