Roscoe, you are correct, different numbers, and maybe that is why it was re-proofed in 1955. At least the bolt is a Mannlicher Schoenauer type bolt as it has the lightening cut in the guide rib and the bolt hold-down cam behind the handle. Several of the well known British makers offered MS rifles with a round bolt knob and as it is a trade rifle it looks like someone just replaced the whole bolt, maybe because the bolt face was pitted.

Matt.