This particular example looks underinked, that is, too little ink was applied to the plate. Probably the inking vessel ran low
Wasn't the ink applied with a roller then wiped? Wouldn't the lack of ink have been noticed? If this stamp was in the middle of the sheet of 100, wouldn't the lower part of the sheet have been un-inked impressions?
When did the sheet get overprinted? I don't think it was while the carmine ink was still wet, or the typeset plate would have smudged and blended inks. Those impressions without carmine ink would now get blue SPECIMEN printed on them, before becoming printers waste.
More questions, isn't stamp paper accountable? Wouldn't Continental BNC have to keep some record of how much waste they had in a day?