It's likely some combination of parts. Like, we can build 3000 trucks with the sunroof and 2000 with the 33-gallon tank and 1000 with the MFT. As a simplified example, they can either build 3000 trucks (1000 with all 3, 1000 with sunroof and 33 gallon tank, 1000 sunroof only) OR they can build 6000 trucks where the features don't overlap.
If you do that same analysis over all the parts that go into the trucks, you'll see builds with all features (and all combinations), but there is optimization going on to get the most trucks built with the "limited" supply of certain parts.