Longbranch no4 mk1* markings help?

Hi there I have a 1943 longbranch no.4 mk1* its all original with matching serial numbers,I have been able to figure out what most of the markings on it mean but one has me stumped, just forward of the magazine under the forestock its capital letters K and B side by side. I know longbranch often superimposed a B over an L but on this particular marking it looks just like a B. I have tried to photograph it but my camera not up to scratch. Any help with this much appreciated,thanks.

It sounds like one of the many inspection stamps I’ve seen on original examples. It’s a good indication that the stock was originally fitted during assembly at Long Branch as apposed to during refurb.

Thanks very much for that information that marking was driving me crazy. All of my 1943 no4 mk1* seems 100% original all matching numbers and when i bought it there was a storage tag on it and if that anything to go by it was in storage since 1960.