dilydaler,
440.6(A)tells us to size the conductors based on the nameplate rated load current. The exception says: "Where so marked, the branch-circuit selection current shall be used instead of the rated-load current to determine the rating or ampacity of the ....branch-circuit conductors..."
440.32 tells us to size the conductors at 125%.
Assuming your AC unit was not "so marked for branch-circuit selection current", then the #10s are good for the 23.9 x 1.25 = 29.875 amps.
The #10s could have been used, IMHO.
