Very early slings with the wide slide can be a possibility that some were changed during or before issue. I can be 99% sure they were not produced that way.
I have had a few 1943 with the narrow slides too. I even have an OD, new, original folded from box, with a narrow slide. It had to be a production error. It looks like a very late sling with the C tip modified in a vice. I suspect it was a certain maker because only a few packed the slings in boxes.
The narrow slide is a disaster when it comes to adjusting the sling. The 1960's nylon sling (produced again in 2002) usew two of the narrow slides. It works fine with nylon, not good at all with web.
As far as markings of 1942, I have the contract records but I will not publicly let out the period of production. Keep in mind that there are fakes slings, fake slings with fake markings, and original slings with fake markings. One better know the details to survive in authenticity.