>Do any of you have experience with using scratch-away
>markings using the silk or component-copper layer?

I know I have seen 7-segment type numbers in etch, but have always assumed
they were modified as the PCB masters were updated. Maybe you could use an
8888 type marking, and noticably mark appropriate segments with an engraver
or dremel or similar, to indicate that that segment is "erased" to indicate
the number, without necessarily removing the whole segment.

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