1917 Enfield Bolt Letter Stamps Question.

I have not found any explanation for all of the various letters stamped on Enfield bolts. From A to Z, every letter in the alphabet seems to have been stamped on bolts at some point in time.
The meaning of E, R, W, USMC, K, and N.S. are well known and have been discussed here in the past. But what about all the other letters that show up regularly on 1917 bolts. These are large letters that appear on the top side of the bolt with the Ordnance stamp.
I do not think they are Weedon Repair standard stamps.