Drums are able to get to their rated life fairly easily, they usually end up with a (very) slight density variation pattern in greys that my users never complain about. I can see it when looking at the surface too. It's a bit like those stereogram hidden pictures from the 1990's.
Developers, they are usually pretty much unusable by the time 600K comes around. The coating has worn away, the density of greys will mirror the pattern of the coating which looks patchy, and the spillage will be everywhere inside the device.
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