Unless my mind is failing, in 67 Nail 1x was Command, 2x was Staff, 3x was instructor, 4x thru 9x were jocks and when the FANs started showing up they were 10x.

Larry--at NKP in 68-69 the callsigns were as follows:   pilots--double digets--assigned as to the next one available--when someone rotated the number was available for the next guy that came in.  FAN's were 3 digets--all starting with 1-----until---about 1 May 69 when the OV-10 folks stopped being Snort and became Nail with the 2 diget designator, the 0-2 pilots picked up the 100 series callsigns--just added 100 to the one they had, and the FAN's became 200 series--just added the 2 instead of the 1---hope this helps.
E. K. Loving
Nail 137/237

Can only help with Nails as of 68 and 69...

All 1XX call signs were front seat

All 2XX call signs were GIB/side seat FAN's

All 3XX were special one mission designators

All call signs were followed by a two letter E&E
reference, usually first initial of first name and
initial of last name...

Thus when I left for the big BX I was flying under
              "Nail 213 (AM)

Col Al Matheson

Cricket was the name of the  program that the 23d was created under. They flew under the Gombey Call sign from NKP until fall 66...we can't seem to nail down(pun intened) the actual date when it was changed to NAIL which the 23d utilized until the squadron was deactivated in 75.
NAILs had ops in ALL AOs to include TDYs to SVN and played a major role  in Cambodia. There were FOLs at U Tapao  and  Ubon. But...the  UT birds flew under the  Zip Gun Callsign.
The Ubon OL was a major operation to support souther Steel Tiger and all the way to the Au Shau Valley.  Trying tto get dates ofwhen it opened and when it closed.