I'll tell you what has happened - probably, as I see it. It is what we call a 'ringer'. That is it certainly started its life as a Mk1* XL XXXX serialled Long Branch rifle and for some reason or another, probably for nefarious accounting reasons, it has been 'swopped' or 'ringed' for a Savage Mk1* rifle, serial number 49C 0960 and THAT rifle number, 49C 0960, has been slightly wrongly engraved with a scratchy-pen on the body side.
It used to happen with us a fair few times but NOT for nefarious reasons I hasten to add. 60 rifles would come in and go through the bead blaster, phosphate and paint system. A couple would come out with the serial numbers obliterated - usually Fazakerley guns but BSA too - So you look through the AFG-1045 to see what the numbers were, then number to suit! Hence, that particular rifle might have come in as AB 12345 but it's gone out as BC23456. But importantly, the quantity remains the same.
Easy........