1923 Imperfs Question

I have this 578 with trimmed edges and was curious if any rotary press imperfs were known as well as flat plate printings.
Does anyone have any good reference material regarding imperfs, particularly in how they are separated from sheets, who separates them, is a different paper used compared to their perfed counterparts, etc..








The most likely scenario here is that it's a trimmed 578, but I'd like to know if there are any ways to distinguish perfed vs. imperf beyond just looking at the edges.

Any and all information is greatly appreciated.

Try www.stampsmarter.org , very good website. No, the best.....


Peter

For U.S. rotary press printed stamps, there are two different imperforate stamps:

Scott # 459 (coil stamp)

Scott # 631 (sheet stamp)

Imperforate stamps should at least be collected in pairs or bigger mutiples.

This is mostly to show the imperforate in between stamp detail characteristic.