Pivi - to date, I have not seen any .440 Cor-Bon round with the correct headstamp. All I have seen have a .50 AE headstamp. I have three samples of their prototype and five examples of the finalized, commercial product, including the box for one of those. Again, all have either an IMI , SPEER, or Starline .50 AE Headstamp. The first two of the prototype rounds I got had the Speer headstamp - a new, formed empty case and a dummy round with no primer. The loaded Prototype round in my collection has a IMI headstamp.
The prototypes are from the era c. 1996/1997. They have a higher shoulder (shorter neck) than do the production versions of .440 Cor-Bon. The shoulder starts at approximately 1.01" from the head. My production round for which I have a box was from lot number 2003, dated on the box 02/23/99. However, I received my first production rounds with Speer headstamp in 1997 and 1998, with IMI headstamp in 1999 (the one for which I have the box) and ones with Starline headstamps in 2001 and 2002, so that probably represents a fairly accurate sequence of use of the various makes of case.
The production version’s shoulder begins about 0.963" from the head (please accept these measurements as approximate. Due to a chronic tremor in my hands, it is very difficult for me to take extremely accurate measurements of these features on a cartridge case, where the case is not virtually clamped in the dial indicator).
There may be other versions of the .44/50 AE. To the best of my knowledge, all of mine are from Cor-Bon, and are not the product of any outside party.