The last observed serial number in the final batch of Super-Multi-Coated 28mm TAKUMARS (43872) in 1975 is SN 8419613.
(Beyond are 11 observed single lenses of 11 different focal lengths with serial numbers from SN 8474600 to SN 9924577.)
Serial numbers of M42 lenses begin in 1957 at 13000
Numbers available 1957-75 = (8419613-13,000) = 8,406,613
(= ∑M42 + ∑gaps + ∑6x7) (because M42 and 6x7 share the same SN series)
= 7,636,884 + 410,262 + ∑6x7
And; 8,406,613=7,636,884 + 410,262 + ∑6x7. So; ∑6x7 = 359,467.
*Approximately 360,000 6x7 Takumar lenses were made from 1969 to 1975 (inclusive). (Mean 50,000 p.a.)
(A second method; adding early estimates of totals in P67 Field Guide gives a total of nearly 300,000 6x7 lenses.)
*Approximately 7,640,000 M42 Takumars were made from 1957 to 1975 (inclusive). (Mean 402,000 p.a.)
These kinds of estimates, based on observations, largely satisfy questions I set out to answer. They are as precise as most could need. There now exists a (still growing) list of 5,214 batches showing the order of production of, and numbers of each lens model made in each batch. It’s an archive for anyone interested in this history.
Now I intend to gather less numerical data on lenses and to work on their physical aspects.