Stamped Envelope, U312

I'm not sure this is the correct Forum for my question, but I hope you overlook it if I made a mistake. Following is my question: On a prepaid stamped envelope,U312, Two Cents,Green,Washington, I noticed an oddity that I couldn't find on any of the other three same envelopes I saw. There is a small white line through the right line of the letter "W" in TWO. I have attached three pictures and would very much appreciate your opinion on this. Thank you very much.
hawkstamp

I have seen this die variety before. In fact, I think I have one, but am unable to put my hands on it at this time.

There are many die variations for this envelope (the 2 cent oval Plimpton & Morgan family beginning with U311). There is a list of some of these die varieties in the back of the previous edition of the UPSS 19th century catalog, but it was put together before the days of scanning, and is not a satisfying resource. This area is ripe for some detailed research work.

Most die varieties are a result of multiple working dies. Your example, however, is a result of damage to the die.

Based on one example it is not safe to say die variety. However, for your example, it was documented by HS Dickinson as die variety B-20. Dickinson identified and numbered 29 varieties of this die. Some folks were continuing this research but have never published anything. There is some contention as to whether these are true die varieties or just repeated inking freaks.

Being new to stamp collecting (relatively) I am learning more every day. But that's the great part about this hobby of mine. I have learned so much in the past two years, not only about stamps, but history, people and the world as a whole, and I sure enjoy every minute of it. Thank you very much for taking the time and helping me out.
hawkstamp