The earliest Maeda Industries date code I have seen reported is NC, but this was on a freewheel on a 1972 Katakura manufactured frame for Nishiki Professional.
Nishiki Professional post
The earliest Maeda Industries data code I have seen is NI, again on a freewheel.
maeda 8.8.8. freewheel
Edit: I think the derailleur date codes came after the freewheels.