The scratched numbers are scratched into one of the gold strips. Looks similar to using a rotary engraver.

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Here to learn more so I can recycle more
My grades are my own opinion and not an official grade from Boardsort

Thanks Marked141. I'm thinking this a "homemade" project. Could be AARL. Or a "school" project. Even a research laboratory. I had a friend who had a side business. Making custom PCBs for major corporations. His specialty was taking a known finished PCB. Then miniaturizing it. He had his own laboratory in the basement of his house. Even had chemical etching tanks. Everything.
Thats why a little background on those chip carriers would be interesting. Enjoying the search.
Here to learn like everybody else.