In terms of my T-16 post, I was referring to new production vehicles and that they transitioned how they would leave the factory over time. No doubt my former carrier would have had the 4-inch until the end of the war and never been converted for a 2-inch mortar. The troops in the field would have kept and used whatever they had since obsolete didn't move to the obsolescent category until after hostilities were over.
And Nigel's three book series is an excellent photographic study of the carriers and kit
Image attached in my live 4-inch which didn't go with the carrier since its an ATF registered short-barrel rifle here in the States.