Help With Uc2 Stamped Envelope

I have a copy of UC2 (as best as I can determine, see photo) however I'm having some difficulty with the watermark (photo provided). According to Scott's specialized the 1923 watermark doesn't appear with the date straight across the lower portion of US, however this is clearly true with this envelope.

Any help and education with this will be greatly appreciated and I apologize in advance for any "stupid" questions.

Thanks, Eric

Looks like watermark 30A, interlocked U and S with 1929 across the bottom and a portion of the top of the S removed. The modified S indicates an official change in the weight of the paper. The watermark you picture does seem to be curved near the 1. Look for another watermark on your cover. My Scott Specialized (2013) doesn't say anything about the watermark on UC2.

The UPSS 20th century catalog lists AM8, a size 10, with watermark 30A, at $6.00 used. UPSS size 10 is 89 X 160 mm.

I agree with Jobi01, it is watermark 30A. Taking measurements off the screen it would appear it is a size 13. The complete UPSS number is AM9-30A.

There is no 1923 watermark. Where in the Scott Specialized do you see it?

Ahhhh. There is my first mistake. I read it as 1923 but it's 1929 and with the shortened S it is clearly 30A. Thank you! I need to train my eye. Thank you all for the help and education :)