I've just been looking at a spreadsheet I knocked up showing transtlantic flights in 1969. Its certainly true that flight numbers were more likely to follow the w/b odd principle in earlier years although this varied by airline. In the 70s odd numbers were mostly westbound but there were exceptions. W/b Europe - Anchorage were mostly even (but then TYO is eastbound). QF 530 operated LON - SYD w/b. AZ. LH & TP used even number w/b transatlantic. Today BA uses odd number for outbound long haul & even nos for outbound short haul & v.v. regardless of direction. As an aside I believe in the 80s you could identify the aircraft type on a Delta flight by the range its flight number was in.