US Unused Scott 272A With Usir Watermark

Recently purchased as Scott 272, 8¢ Sherman, unused, hinged, no gum. I believe it has the USIR vertical watermark with a portion of the S visible on the left end and the I visible on the right side. Will be sending to PF on Monday for certification. Thoughts?

Front of stamp:


In watermark fluid:


Annotated:


Dry without watermark fluid:

Puzzled by your chain of thought how the USIR theory is supported by a broken "P" illustration. But moving on.....

From the illustration of the watermark in Scott, consider that the USPS design repeats across the pane and there are two "S" characters in the basic text. Thus rather than your stamp being from the red rectangle, it instead is the green rectangle which contains a portion of the other S and the top of the "U" as .....

Fully agree with John and will add that without a clear "I" or "R" it won't get a cert.