Probably because the "availables" didn't have rear fenders and the "not availables" did.
Bill -- That could very well be the case. I have seen two earlier MY 1-tons (see pics below) that were duallie pickups. The '46 is owned by Jim Carter and is a beautiful restoration. It is very factory.
Not sure about the '38. It appears to be a factory job and missing its fender extensions.
I have never seen, smelt nor heard of an AD factory 1-ton Duallie. The data book would tell us that they were not made.
