I am assuming you are talking about mint stamps. The imperforate stamp may have been cut from the pane of 6 (735a) or from a full sheet of 25 panes of 6 (768a). From the basic single stamp, it is nearly impossible to distinguish between 735a and 768a, unless you personally know what it was cut from. Most collectors who want to distinguish between the two, collect 768a as a gutter pair.

768a exists gummed, but that is not a reliable way of IDing it.

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