It might have been unused muffer. i remember seeing bundles of them being sold at gunshows years ago. The style and font certainly looks like mine pictured. Had another two like it but both rifles are sold. Haven't seen it on a cocking piece before. I thought I had pictures of cut offs and front sights but can't find them now and all the rifles are gone. I did also have a 1927 Lithgow with MA27 on the sight protector so there seems to be no rhyme or rhythm with the date stamping. The first use of the MA stamp was 1926 according to Ian Skennerton and I would agree with that. I had a very good assortment of 1926/27 rifles that appeared very much unaltered and these had a mix of lithgow star and MA stamped parts such as nosecaps, trigger guards, sight protectors, sights, front bands and butt plates. One area i don't agree with Ian Skennerton is the use of knurled cocking pieces. I feel the change over from rounded style to rectangular milled on newly manufactured rifles was the same time as the MA stamp in 1926 rather than 1941.
Here are the cocking piece markings on my 1935 Lithgows