Hi sapphireguy, I do not think your stamp is 10A but rather an 11A. While the image quality is poor, you can definitely make out a guide dot in the lower right corner, a single line recut in the upper left triangle and a right inner frame line that extends well up into the upper right triangle. I did a quick run through of the plates and believe this stamp is most likely from Plate 2L or 3 making it an 11A. I also went through plates 0, 1E, 1i, 2E and 5E (plates where the 10/10A came from) and did not see a good candidate with the three features described above. To confirm this for sure I would need to have a higher resolution image of the stamp. It's also worth noting that the pigments used for the Orange Browns of the 10/10A do not typically show signs of sulphurization like has happened with your stamp. If you can post a higher quality scan of the stamp I would be happy to try and plate it.