From the point of view of his banking institution, yes, your father-in-law and the Iron Bar Man are their self-same identities -- but I see what you're getting at: for the purposes of proving he is who he is, a man's store of proof is impaired or changed over time.

That is true of any identity measure. I would argue that those cases illustrate the importance of improving the accuracy and affordability of biometric identity measures, but also, by extension to other kinds of accident or mishap, the importance of layering the modes of measure. I'm all for stacking the modes if it means decreasing the likelihood that someone can pretend to be me.

People know my father-in-law for..

Hmm. This starter might actually be the only real measure: who you know. :)