Mitsumi date labels
Mitsumi “price label” stickers typically fall into two formats: YYnnnn (six-digit), and nnYYnnnn (eight-digit) — the year digits always correspond with IC codes and case mouldings. The meaning of the remaining digits isn’t certain. My guess was that they were serial numbers, in the form YYnnnn (six-digit) and WWYYnnnn (eight-digit). However, rzw suggests that format is nnYYMMDD (and possibly YYMMDD for the six-digit form). In the latter case, the stickers are thus not even serial numbers, but simply manufacture dates.
Examples such as my Apple Keyboard II and MouseFan’s Burton keypad (eight digit) and Kevin Schoedel’s Apple M0110A all fit either theory; thus far, no sticker has been found that does not contain a valid date.