Aircraft of that era were originally registered by the then CAA with additional prefixes after the N for USA registered aircraft, such as NC, NR or NX. Your father's logbook would use NC then. These older aircraft originally registered with a dual letter prefix can retain it as such aircraft may be recovered and refinished, but use just the "November" for N---- with initial radio call up to a airport with a control tower.
In accessing an N registration, or NC or NX, etc on the FAA website-only enter the numeric/s and any subsequent alpha's in the N number, NOT the initial alpha/s. Example: N503UM would be entered as 503UM to see the registration information. I took my FAA check ride in N503UM many years ago.