One reason it's confusing is the 1971-1972 floating J serial numbers on page 399 in SCSW 3rd has a slight typo . . . it should read 1J1 to 999J99.
Note that the 71-72 floating J period has a total of 6 digits (including the letter J). If the s/n has a total of 7 digits and starts with 1J, it could be from 1983. How's that for being confusing?
Russ
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