Well, the fact that the nosecap number matches indicates that he had some or all of the original parts. But if as you say he had it in a sporter stock, it was probably the case that the old original wood was pretty damaged. So, having all the original hardware at hand, he got hold of some nice new wood and put her back together. There is no way that wood is from the original 1918 issue. It is just too purdy!!
All in all though, a great find! Count your blessings!
My 1915 BSA (no star) was FTR'd in 1944 (or at least, the barrel is a 1944) and the bubba varnished buttstock was stamped 1941. My nosecap is NOS (New Old Stock) unnumbered, because the original nosecap is God knows where. The windage adjustable rear sight is from a 1913, and the numbers don't match (obviously). The piling swivel is from an Eddystone. The rear volley sight I bought in the EE, and the forward volley sight is a repro (still waiting for it). The bolt has a different number, does not headspace correctly (still looking for a solution to that), and the round cocking piece sports a Lithgow star. The rear sight protector is also from a parts bin. The forestock is Enfield, 1913, inlet for the volley sight, and NOS (YAY!!). The front handguard is black walnut, while the rest of the wood is English walnut. In short, my rifle is all mixed up! And I have had the time of my life restoring her!