NEC PX-50XM4 series Service Manual page 339

(3) Contents SERIAL LABEL printout
(24L44731)
*The model name shall be printed out at the upper stage.
*The serial number shall be printed out at the lower stage. (Manufacture number control rules CPD-Standard-B102)
The numbering system for the serial number shall conform to the following:
4 7 0 1 2 3 4 9 S
Control symbols:
Production base:
Serial:
Model name:
Month of production: January ~ September = 1 ~ 9, October = X,
Year of production:
7-30
S → A → M → T → Z → N → K → U → C → W → J → P
When all the symbols are used, the numbering order returns to S.
9 (NEC Nagano)
Serial numbers of 0000 ~ 9999
To be reset to 0001 each time the month of production is changed.
Fixed to 0
November = Y, December = Z
The lowest digit of the year of production
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