The ON or NO is the tank code while the codes in the list posted is the assembled radiator codes. I have never seen a chart with the tank codes.
The codes (Camaro perspective) are explained by the CRG at
https://www.camaros.org/coolingsystems.shtml#usage
I believe my '68 has the original UP code (400 w/AT) Harrison. It also has the ON/NO tank code. Was the ON used for other radiator assemblies? I don't know. Perhaps a good old radiator shop would have a Harrisom parts cross reference book??? I had my original radiator recored in '78, 86, and 11. The UP code tag/plate was missing so I had one added in 2011 during the restoration.