First issue revenues were issued in 3 types: imperforate, perforated, and part perforate (imperf either horizontally or vertically). Not all denominations were issued in all 3 types.
What I mean by "not trimmed" is that I do not believe it is a perforated stamp that has been trimmed down to fake a part perf, which happens a LOT out there, since the part perfs tend to be worth a lot more.
That is why imperfs and part perfs need extensive scrutiny:
1. Ideally you buy them in multiples or on document
2. The imperf margins need to be large enough to preclude trimming
3. The color, impression, and paper need to be appropriate for the period in which the part perfs or imperfs were printed, as opposed to later printings which where primarily perforated only.
4. The cancel date can be used to (usually exclude, but in this case include) a stamp as being genuinely imperforate or part perforate.
Some of the differences between a perforated stamp and a part perf or imperf of the same design can be ASTRONOMICAL, e.g., R84c (the perforated variety) which catalogs $20 and R84a (the imperforate) which catalogs $8,000.
Here's a good example... the document I showcased in this thread:
https://goscf.com/t/16655The reason it's so desirable is that it is an absolutely genuine example of R83a, the imperforate $2 Probate of Will. It catalogs $6,000. The perforated stamp catalogs $80.