Can't admit to too much surprise that I didn't come up with a totally original revelation. But it was a revelation to me that an air pressure gage on a bike tire pump could be off by 28%. Can't be many like that, I must have been lucky.

Here's the part that really surprised me- My LBS guy said that he had seen rim tape failing like mine did but it was virtually always multi-years old. I thought rim tape was forever but it turns out that it is a maintenance item and has to be replaced occasionally (if you ride that long on high pressure tires). When I change tires, I'll start checking it.