Bill - Thanks so much for posting the photographs of the three string grooved self nock arrows.
Your self nocks are surprisingly similar to mine. It appears that the same process, machine and/or person was used to make them.
Yes, I have seen several old ink stamped arrows. Some by the manufacturers and others by bowmen. Hard to say who Walter N. Molzen of Newton, Kansas was, but perhaps we sill get lucky and have someone Kansas tell us more about this gentlemen.
The two Zwickeys would date circa 1939-1941, the Ben Pearson would date 1942. As you say these broadheads could have been put on the arrows at any date.
John - Bill's two Zwickey's are convex cutting edge sloped shoulder models, much narrower than the straight cutting edge Unknown #20 (Bear's Special Order). Note on Bill's 4 blade that the bleeder is cut from the right side, this was the original die.... All Zwickeys made after these original heads, (1942 & later), have the bleeder cut from the left side of the ferrule, that includes the 4-blade Unknown #20 (Bear's Special Order), which I am sure you have noticed.
Ted - Very interesting observation that the small side of the nock is in line with the cock feather and could be used to index the arrow.
I'm sure you have seen the old self nocks that are stepped, meaning one leg is intentionally and noticeably longer than the other. At one point, Glenn St. Charles used stepped nocks. Glenn's old hunting pal Bert Wallis used them too. Just checked one of Bert's stepped nock arrows and see that the string groove is also off center. However, the cock feather side is the thicker side of the nock, but also the shorter in length. Both Glenn's and Bert's arrows had no string groove extending forward down the shaft.
Thanks to all who posted. Hopefully we will all learn more from additional posts and someday be able to identify who made these string grooved self nock shafts.