Canada continued...

Line perforating machines sometimes have loose perforating wheels which created varieties like #87e (horizontal pair imperforate between). At other times an alert pressman would take the finished sheet over to a perforating machine to correct the missing perforation holes, especially if the missing perfs were in the margins. These compound perforations occur occasionally on the stamps of PEI but rarely on the stamps of Newfoundland.

Scott and Unitrade both list (but do not price) #87h perf 12x12x12x11 suggesting that one or more examples are known perf 11 on the left hand side. That fact would fit with the assumption that the known examples come from column one. Yet, this pair proves that the compound perfs come from both the left (hence perf 12x11x12x12) and right of a row of perforations measuring 11 between column one and column two of the sheet. (Scan a)