Yes, could have been a ‘65 order and ‘66 construction date. It was indeed a special order (per my Dad) specifically for the left-handedness, no etching, and wider nut. (I measured to be sure it is 1 11/16”.)
I did swap the strings around just to play it for a bit, but it’s not being left like that. (My left-handed son will end up with it.)
Employee error is definitely another possibility for the 2 serial #s.
Looking inside it appears they applied the 2 braces below the bridge pad angled the opposite way as a right handed guitar, and the bridge route is obviously angled opposite for intonation. Other than that I can’t see anything particularly different.
Thanks!