The 4th axis interlock is actually on C01. So if you see something referencing C03 the control may have the PMC feature which means you need the prints or ladder to determine where the signals would get connected.
I'm guessing what it is looking for is "4th axis unclamp confirmation"
C03 pin 36 is 3rd (Z) axis interlock with no PLC. So this also points to the control probably having a PLC