Show Your US 1851-57 Imperforate Stamps

Good day all, I'm some what stuck, and can't figure out what position this is, cert says its a US No.10 but I believe its a No.10a. Position 9L1e. its a EKU I believe. If anyone can help with this, it would be much appreciated. and thank you.

Considering that 10A was added to the catalogs relatively recently (2008?) the PF would have called that a #10 in 1985 when your certificate was issued, even if now it is known as a 10A.

Plating AI says it is a 10A position 9L1e with a score of .839, or an 11A with a score of .833, or in 3rd place a 10A position 9L1i with a score of .827 and so if the PF is correct that it is a 10 family not an 11 family then 10A position 9L1 appears to be the consensus. (Did you come about 9L1e on your own or did you use Plate AI? if the latter, then my running the same tool does not confirm the consensus).

Regarding EKU, for clarification, it is not an EKU for 10A (which was July 1, 1851). It is described as the earliest known use of any postage stamp in Chickasaw Nation, Indian Territory, which is still pretty cool.

Fort Washita - with an OB 3c is a terrific postal usage, congrats.
I do not know if the EDU still stands for this I.T. but its early and very cool.