I"m not sure what this obsession with evidence is
This happened quite a while ago. I'm guessing around 79--> 80. I just forgot about it (in the trunk) and it turned really cold that night. So this many years later, I would have noticed an out of tune condition along the way. It desperately needs a re-fret though (original frets). If I was still living in Ontario that would be no problem because they are many expert technicians there. But Nova Scotia has barely 900 thousand people in the whole province and is less sophisticated. Here's a pic - you've seen thousands of these.