I also like to now those BROOKS stamping. I looked into B-15 Champion Standard from 1965 Paramount stamped "C 62" PAT. NO. 662070.
For additional info, I also have;
B-17, Champion Narrow "B73" MADE IN ENGLAND, B-17, Canpion Narrow "A73" both looks alike, no difference in looks.
So, I have "A", "B" nad "C" in 60's to early 70's. But also I have Professional w/large rivetts marked "A 80" What are those A,B,C,???
KEN TODA, High Point, NC