Imperf between

Imperf between is an error of a normally perfed or rouletted stamp pair or strip. It is imperf in one direction only and may involve just two stamps or all the stamps in a pane or sheet.

It is only a true error if the imperf part has absolutely no perf/roulette holes and absolutely no trace of dents from the perforating/rouletting process. If there are such unpunched perfs/rouletting, the pair is in the freak category and not an error. A row of perfs that disappears for just some of the stamps in a pane or sheet, is technically a freak rather than an error.  File:US 3c defense.jpg 

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