It's fascinating that English Electric went to the trouble of building a one-off FEDD body. They probably hoped for a big order, which didn't eventuate. HA9432's original body BB2256 was in 1937 mounted on another of the same batch (HA9408), according to my Midland Red body lists (ex-Hardy).
I suspect that it was Midland Red trying EE out, rather than a speculative build. Its body number immediately precedes the 65 EE bodies for SON chassis (A1877-1941, CHA 501-565).
The 15 Trent identical versions of the BHA FEDD had chassis numbers sprinkled between the Midland Red ones in the BHA 316-332 range, although their body numbers (BB2535-2549) were together. It has been suggested that Trent was in urgent need of these buses, and took a batch from the bodymaker as soon as possible rather than wait. The chassis of the final 15 of the Midland Red batch, BHA 820-835, were effectively the Trent - ordered chassis.
Had RC 3333 been secured, it would probably have been restored as Midland Red BHA 343, the number that chassis would have carried if the Trent ones had come together at the end of the batch.
Midland Red had 'tried out' Metro Cammell with 1932 body BB1952, a B34F body for IM4 A1344, HA 8295. This left that chassis' intended body, Brush BB1951 as a spare, which went on A1366 (HA 8291) in 1934, releasing BB1947 which went onto A1363 (HA 8288) in 1936, similarly releasing BB1944 which went onto A1346 (HA 8270) in 1940. (Etc, etc).
Metro Cammell DID build a speculative "FEDD" body though, in 1935, having 'improved' the BMMO design to include four rather than five bay construction, and a forward-sloping rear end. Midland Red must have been uninterested in this project though, for it was mounted on a Daimler COG5 chassis and finished to the specifications of the time for Birmingham Corporation, who subsequently bought the bus as their 94 (BOP 94). [The '90' series fleet numbers being used by demonstration and experimental vehicles]