I think when they are saying DIFERENTES PERFORACIONES it's because of
the Line Perforation method used which led too differences in the corner alignments...? ;but that does not explain the difference in perfs.
Maybe there were some perfed that way.In your stamp the horizontal perfing is less regular than the vertical perfing..mystery
Scott 18 ,1867: $ 7.00 used ,maybe more,I have an old catalog.