Not all JSM stamp have the vertically running perforation! As we could see in Rodolfo's sheets of the 12c the perforation goes from left to right! It may turn out that this was the predominant situation in the period 1923-1930!
It is difficult to find good examples of the right bottom/top teeth being broader or thinner! What may be an indication of this type of perforation is that the stamps often badly centred! The vertical perforation holes touching the design!
The stamps are on Wiggins Teape paper [from England] with a parallel watermark, the direction of paper is vertical! This WT paper had a rather closed granulado [not so clearly visible rhombs] during 1926-1927, but from 1928 onwards the granulado [the rhombs] are very clearly visible and the indents oft he rhombs as well!
to be continued ....