This explains the difference between short and long haul, with short haul being even out, odd return, and long haul being odd out even return, but still doesn't explain the inconsistency on long haul routes as to whether the return is the outbound's number +1 or -1. Like I say, on the lower numbers, like BA 5, the return is BA 6, but on bigger numbers like BA 143, the return is 142, not 144.