> Once they were a sort of version number, so I put them in
> the source code

That's an option I may use. Org the code to start at 0x200 and
hide it with CP_75, which will return 00 for the locations from
200 to 7FF when read. ID and product notes (and possibly even
phoney code) can go in the readable lower 1/4 of program memory

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