Thank you Matti.
This was from an ULTRA message (CX/MSS/R483(C),21:
To AMC [Air Movement Control] Unterschlauersbach from AMC Lechfeld, dated 4/3 [1945]:
Request landing report of 7204 BP+FO. Took off from Lechfeld at 0735/(smudge)2.
So I wonder what "7402" meant if it wasn't a Werk Nummer? Another aviation mystery!