The Scott Specialized Catalogue states the following with respect to part perforates:
Part perforate stamps are understood to be imperforate horizontally unless otherwise stated.
Part perforate stamps with an asterisk (*) after the value exist imperforate horizontally or vertically. As a general rule, part perforate first issue revenues that are imperforate vertically are considerably scarcer than their imperforate horizontally counterparts.
The difficulty with the last statement is that while the catalogue value represents the value in the "normal" orientation (imperf horizontal), sometimes the scarcity of the opposite orientation bears absolutely no relationship to the scarcity of the normal orientation... so how do you go about valuing the imperf-vertically part perfs? In a perfect world, the catalogue would have separate values for each orientation.
The catalogue numbers that Scott lists as being found imperf vertically is as follows (the ones I consider to be the most commonly found imperf vertically I've highlighted in bold):R1b (1-cent Express)
R3b (1-cent Proprietary)R5b (2-cent Bank Check blue)
R6b (2-cent Bank Check orange)*R9b (2-cent Express blue)
R25b (5-cent Express)R33b (10-cent Certificate)
R36b (10-cent Inland Exchange)[/b]
R44b (25-cent Certificate)*
R69b ($1 Inland Exchange)*
* I question the existence of these imperf vertically. If you have examples, I would love to see them. I'm pretty sure that R69b are late-printing EFOs now listed as R69e, not legit part perfs.
Stamps not designated as appearing imperf vertically that I have seen either multiples of or convincing singles of:
R32b (10-cent Bill of Lading)
R56b (50-cent Foreign Exchange)
Case in point, as I was flipping through a selection of revenue documents at Chicagopex, I encountered the one below, which made me do a double-take. The 10-cent Inland Exchange part perforate (R36b) is a relatively common stamp, cataloging for $4.50... but for the life of me I couldn't recall ever having seen one imperforate vertically before.
It turns out I do have a lone example, acquired in back in 2015. Perusing all of the usual online stamp venues and dealers turns up zero examples that I can find.
So this is a case where I believe the scarcity is FAR greater than what the catalog value implies.
Do you have any examples of R36b imperf vertically? If so, please post them.