Geoff
Correct; 210M did not start production until 1977, but according to Cessna data, the serials were assigned according to FISCAL year (not CALENDAR year).
I do not know what FISCAL system they used nor at what point in production the serials were assigned, with regard to place in the production line of the airframes.
(They may have tinkered with line assignments vs. dates?)
210 Serial Series
210 and T210
All with prefix with: 210
210L --> 59503 thru 61573
210M --> 61574 thru 62954
T210F thru T210J series only had prefixes: T210
Production years (Fiscal)
210L 1972 > 1976
210M 1977 > 1978
T210L 1972 > 1976
T210M 1977 > 1978
Hope this helps
John
PS - I post again as soon as can I check some FAA record on fiche. Haven't had
my wake-up coffee yet :