Help Identifying Versions Of U10

Greetings all. I am new to this forum and hoping you all can help. I have several entire 3c red Washington stamped envelopes that I think are U10 but would like to confirm and determine die type, etc. Are there any guides/articles out there you all would recommend. Scott Specialized doesn't seem to go into the variations of U10 unless I'm missing something. I've attached a couple of them below. Thanks in advance.

Go to UPSS.ORG/code/epublications. For $13.00 you can purchase a downloadable copy of the United States 19th Century Envelope Catalogue. It will give you much better ilustrations along with more descriptive text.

The aforementioned Catalog of the 19th Century U.S. Stamped Envelopes describes around 31 different die types for the U10.

Perfect! Thank you.

The full link is:
http://upss.org/code/epublications.php