I still use a Redline 2-gall can dated early 1930's for the mower petrol, that has the wrong cap, no big deal, the caps get lost, nicked or swapped around. I have used it for more than 40 years.
As for making them still for the army in 1950's, it should be remembered there were still vehicles in service that were equipped with stowage for POW cans and not jerricans.