1962 Vin Question

[pmeyers]

Recently bought a 1962 C10 and I have a question about the vin number.
The first six numbers - 2C1540.
According to vin decoder:
2=model year 1962
C=2wd
15= 1/2 ton long bed
O- is supposed to be assembly plant- but there is no "O" in the list of assembly plants in the decoder.
The factory tag in the truck lists exactly the same information as the title, so it is legit. Just curious if anyone knows where the truck was assembled?
Thanks for your help
Paul