when there is ambiguous year date code. I'm not getting very far googling.
Both A and B series around in 1977 to 1983. When did A series cease production ? they came in about 1968 When did buffered B (plus unbuffered UB presumably same time) come in? When did Buffered Plastic BP suffix come in ? I seem to remember some not having any suffix, were they "A" or some other series