The B1504 number was reserved for the former A64 and A169 through Malton. It may be related to the 1950s and early 1960s plan for a Malton Bypass, which was eventually constructed in the late 1970s.
It is unlikely the B1504 number was ever used, as the 1979 OS 1:50,000 map of Malton & Pickering shows the current numbering arrangement.
