I just notice one thing. The headstamp was misinterpreted at the opening of this thread. It is NOT “MM 6 41” but rather “9 MM 41” with dates from “40” through “41” known. This is an easy mistake to make if one has only encountered specimens of a single headstamp date. When one sees them all, it becomes obvious that the “6” is actually a “9” and is part of the caliber markings, as not every year would be known only from the 6th Month or Lot Number 6, depending on one’s original interpretation of the headstamp.
Regarding documentation of who made this round, I actually don’t know of any off hand. However, there is simply no argument among cartridge specialists, either in the United States, Canada, or other countries, about the origin of this round. Unlike questions of when and for whom cartridges are actually made, which cannot be known for certain without documentation, specimens of the ammunition itself and its packaging provide solid clues to manufacture. In this case, the boxes it originally came in are all unmarked, but they are the typcial Canadian 64-round packaging for this caliber. Since there was only one Canadian manufacturer of 9 mm Para (Luger) ammunition, and since the characteristics of the cartridges are Canadian, it leaves no doubt who made it.
Regarding the dates, these were found to be spurious when evidence was presented that the first pilot lot of 9 mm Para ammunition ever made in Canada was produced in 1942, with the headstamp “DC 42.” There is other evidence backing up the claim that the ammunition was not made during the years represented on the headstamp. Which years it was made is the subject of argument because to date, there has been nothing but theory and anecdotal evidence, if that is any evidence at all, concerning when they were actually made.
There is no sense me recounting the arguments over dating, as they have all be covered before on this forum, on lengthy threads, as you have seen already.