I would imagine that the machining of the body would be dependent of the machines and cutters you have available. I very much doubt whether factory A would go out and purchase a new machine do cut a certain profile form when they already had machines on hand that could cut something pretty similar that had no bearing on the final product in any case. Think Fazakerley v BSA No4 bodies

Same as Bren bodies from Enfield too. Some sides are clearly machined using up-cut milling while others are machined using what is clearly a slightly untidier down-cut process