see post 243 - original photo by me , posted long ago somewhere in the forum.
on the
"OZS" A & B ; one has rounded edge the other more square. A has longer
OZS than B and slimmer.
Suffix , Prefix are rare too

; later introduced
"A" , do not determine they are A Type
They are used because type B , use the same serial. (suffix )
So Prefix and Suffix have been introduced, to save confusion of same serial numbers.
Years after this ; All have been dropped out. This punching do consumed many man hours.
Today bars , don't have serial numbers except larger bars or dore bars ( 11 kg to 15 kg varies in weight )
The 10 oz standard now was taken out due to cost effectiveness, as labour cost increases.