I was quite wrong. My last comments on the signature configuration of earlier balls led to a small supply of vintage examples from ever helpful suspects. One box of Slazengers was actually dated 1974 and the balls therein were of what I had come to think of as a late decadent type.
Perhaps the lone, grey, bald and orphaned ball I started with is truly archaic. For all I know it matches those that appear in Henry V.
I still, however, regard it as somehow authentic and, as here, continue to mimic the fine curves of its manufacture.