This confusion happened occasionally. It seems to have been the intention to use a 'B' prefix for bicycle contracts, a 'C' for motorcycles' and a 'V' for other softskin vehicles. There were some 'A' prefixes too, from the same number sequences. I can't work out what the intention was there.
However, they sometimes used 'V' for the swd Big 4 contracts such as V3565 perhaps because they weren't sure which category to put a sidecar in. The 16H Norton contract C7353 is referred to in some lists as V7353.