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Yes, that is my impression after a 1000+ razors on it.
Even tape will leave stains on it sometimes.
Rather than lapping it though, I just scrub it with a brush after every few razors, and that has...

Honestly, I would ditch that whole backside concept.
Take a picture of the stamps, then flatten it and use the intended side of the stone:)

And as the others has adviced, go to a finer stone for...