Hi all,
At the aforementioned estate sale, I picked up 3 of the lenses listed in the subject line. Each lens has some white paint-printed lettering on the rear element tube as follows:
+6 AUG 10 1964
+16 JAN 10 1964
+7 OCT 18 1962

The dates are obvious enough, but what about the +xx? Does this describe some level of correction? Might these be product development test lenses?

Thanks,

Scott