It has always puzzled me why the NF12 is shorter than the NF14 as they were fitted out with the same equipment, the only notable difference being the excellent teardrop canopy on the 14 as opposed to the old T7 birdcage.
As a minor aside there was no difference in length between the NF13 and NF11 because the 13 was simply an 11 with some different gimmicks for the Muddle East, where there was no Gee coverage. Navaids for the 13 were a Marconi radio compass and BABS/Rebecca.