What Plate & Position Is This Scott 10A?

Also not sure how they determined that the cover was dated 1851.

A #10/10A from plate 1 being used in July 1852 or later is highly unlikely. There is virtually no chance this usage is later than July 1851.

That Philly CDS and grid look much too dark, though. In July 1851 the hand stamps were bright blue, as seen in the first cover shown on the following page:

https://www.uspcs.org/stamps-covers...t-10-and-11/

If the stamp is Orange Brown then the July 28 usage is almost certainly 1851 and would make it very likely plate 1 early or nearly as likely plate 1 intermediate.

I say "almost certainly" because it's possible to have an Orange Brown stamp used in July of 1852.

Oops, sorry Gary I was posting at the same time. While I was writing I thought about plate 2e. I was trying find the EKU is for plate 2e. Couldn't find anything other than what's in the Chase book.

The stamp shows signs of being a short-transfer position, with the design weak at the top of the upper-right diamond block. It's hard to be sure without a higher-resolution scan. The short transfer strongly indicates plate 1.

Here is a higher resolution.

Here is even higher.

The last image doesn't appear to have any orange in it, but the color of the grid looks more correct. Perhaps this is not a #10a. Does it look orange or red to you?

The last image also doesn't seem any larger than the first close-up. Both look like 600 DPI.

I scanned them this time at 400 and 600. Yes the first images are photos and they show the correct color.

How about this?

The note on the cover says the stamp is from Plate 1E. I see no reason to not believe that. In fact, the photo (color of the stamp) makes me believe pretty strongly that it is indeed from Plate 1E. Plating is best done with better images (1200 dpi) than you have posted thus far.

I have only seen the tandem usage of the blue Philly town with the blue grid killer on 1851 covers. I am not sure if I have even seen the combination go into August of '51... certainly not September.

Thanks Sinclair! You ave been a great help on several of my items.