I don't think there is anything exceptional about Maltby specifically, but any early war rifle will have been around longer than a later example & so will have been liable to a hard service life, FTR & so on. Also, none of the factories producing the No4 rifle got into production until at least mid year, so production totals for 1941 were a lot lower than for subsequent years. That applies to BSA, Faz, Long Branch & Savage as well as ROFM.