Here's what I dug up....
JS23N1B2745xx=1971 01 22
JH23G1B3312xx=1971 - MARCH - 1?
JH23G1B2728xx=1971 - JAN - ??
Oh, oh, found this one that messes up the order: JS23N1B2341xx=1971 - MAR - 04
Soooo....with that process of GUESTIMATION, I make another stab at end January/early Febuary of 1971??? Wild guess...
FYI= Your convertible was made between Pace car convertible #1 and 2, not close in VIN though, just between, JH27N1B266664 and JH27G1B284355 respectively.