My mom bought my first gun from K-Mart in 1978. I’ll bet that record doesn’t exist, nor should it.
I'd bet that the record still exists, probably in an ATF database. When the K-Mart closed (most of them did), they were obligated to turn over their records to the ATF. If your gun were found at a crime scene, they would most likely be able to tie it to your mother, probably within a few minutes. Even though the purchase happened over 30 years ago.
That is why many people prefer face to face private purchases, and is the primary reason that 0-bamster wants to outlaw the practice. If they can track guns, they know upon whose door to knock when they want to pick it up. This really is de-facto registration.