Was my original thought, until i thought, hold on both the F4U-C and D can carry ord.
So why omit the F4U-C from the remodel?
Big difference is MG v cannons.
I would imagine in this case, when you select the "D" you will be able to select the "all cannons" gun package, for a cost, and this will then turn the "D" into a "C" ... so no need to keep the "C" model as a separate object in the hangar.