I hesitate to raise what will appear to main in this august group as a facile question - but here goes.
I have read Richard Oliver's highly comprehensive booklet on the Seventh Series. It explains in great detail the intricacies of the various printings.
I may well have missed it, but I have a simple question: Why print a map with different lettering on the same sheet?
I am referring to the HL designation in column 7: Style of Sheet.
Why not wait until a uniform style could be achieved? What was the rush?
My my layman's eye it just looks cack-handed, unprofessional, the very qualities I would have thought the OS would want to have avoided.
I'm looking at OS143 B which has different lettering all over the place, but the same applies widely.