I'm not aware of any telltale sign on the pogo as such, but I think if were heavily stressed you might pick it up during the PCU change when you try and rig the pogo's. You might find the answer at CMM level? Not to say it doesn't happen but in the 20+ years I've spent working on the 737 I've never seen a failed pogo.
or how would one determine if an input pogo was compressed/stretched during one of the above examples
Would you really need to? Technically it's doing what it's designed to do.
Although the AMM (part 1) doesn't specifically mention a cable break it does state that forces acting on the balance panel will hold the aileron at the neutral position when there are no inputs.
Hope this helps.