The "B" is upside down on my EARLY 1982 Ludwig Hammered Bronze Supraphonic. Always thought that was interesting... then I saw Hoppy's, so you have to figure the first run shells were all stamped upside down... until someone caught the "mistake" at Ludwig and corrected? Regardless...
I was initially thinking that the inverted "B" was for bronze material and the standard "B" was for brass... but it sounds like that theory won't hold and it was more than likely stamp-operator error!