Post-41 really, as there would have been way more 1942 dated rifles made with undated screws than dated. It will only be during the first quarter of 42 production that would have had dated screws for definite, and then it could be a bit hit and miss depending on maker during next few weeks, but certainly by mid way through 2nd quarter of 42 all rifles from all makers would have had undated screws etc., so again different numbers depending on production rates for each factory.