I don;lt understand what pair you mean, but I suppose when on active duty during conflict they would struggle to swap their kit for a fresh shirt. But during leave they would be able to exchange worn or damaged uniform or equipment at the stores at base camp, assuming the army was as efficient then as it is now
As far as I know, the soldiers were issued with 3 pairs underpants, and three pairs of socks and 2 shirts, otherwise the rest of the uniform was one of each article. I don't know how correct this is, but I read it somewhere.