Last year I got a call from Texas (I live in California) from an animal rescue group. They said that my daughter's dog, Sadie, had gotten out and been found by someone who turned her over to them. I was on her Microchip records as being second to call, the original home land phone had been disconnected. So I called the school my daughter worked at, the school secretary informed her, she got a sub and ran over to get Sadie.
After that, she put her new cell phone and address on the chip records, but did leave me on it as secondary.
That is what might have happened to your poor little sad fellow. Or, like you said, it may have just been in records packed away.
I'm wondering why the city or county doesn't keep these records, seems to me that should a dog bite someone, they can find the owner very fast around here by the tags.