Can't help with your query. I lived at New Deleval until 1953, but then I was too young to use the pubs at Newsham, at that time. I notice you have 2 spellings of the surname, - Mosses, and Moses. Are they correct ? There were 2 families living at New Deleval with the surname, Mosey. in the 1940s-50s. All my relatives who used the Black Diamond in those days you mention, are gone now.
However, if you keep digging and posting on here I am sure someone will come up with information which would be of help. As regards the Blyth Home Guard, I have seen an item on the web, and it may very well be here in RootsChat. There are quite a lot of entries in here re Blyth, South newsham, and the surrounding areas so best of luck.