Hi All - I wanted to come back and conclude what I learned from my original posting - and thank Winston for his help. I have learned a lot from the exercise.
The stamp I originally posted looks to be a 10A 57R1E from using the plating site as a guide:
My rationale being the following:
- It looks like a relief A (large border gap at bottom of portrait)
- Lower left borders don't quite meet up
- The partial recut on the left side as Winston originally pointed out.
But I also looked at one other thing - my original scan accidentally left off a bit of the left edge where a tiny bit of the stamp to the left is shown, and its right border line runs over a bit. So I looked at the color sample of the 56R1E on the plating site and it shows a similar characteristic.
Ironically, I removed the stamp from the album and rescanned the back as well:
Turns out that is Dr. Chase's notation on the back and states the same conclusion. I have had the stamp for well over 40 years and guessing I bought it out of an APS circuit book in the 70s. At that time I certainly had no understanding of the notation and over forty years, did not remember any marking on the back.
All in all, I think I am getting hooked on the classics and learning about plating. Grateful to have found this fantastic forum.