The most significant season when ‘goal average’ determined promotion was the 1926/27 Second Division season, that also being the season when George Camsell scored 59 league goals. Boro were promoted with 62 points along with Portsmouth on 54 points who scored 87 goals and conceded 49 (+38) Manchester City also accrued 54 points and scored 108 and conceded 61 (+47). Under todays rules City would have been promoted having a greater ‘goal difference’ Bizarrely though under the then regulation when ‘goal average’ determined positions Pompey’s ‘goal average’ was calculated as 87 divided by 49 (1.776) whilst City’s was calculated as 108 divided by 61 (1.770) and is therefore recorded that City were denied promotion by .006 of a goal. As far as I’m aware this is the only occasion that a club was either promoted or relegated by ‘goal average’ where ‘goal difference’ would have given a different outcome.
Although the current system was introduced in August 1976, the Football League, but not the Premier League, made another change in August 1996 whereby ‘goals scored’ became the criteria. The 3rd Division title in the 1996/97 season was won by Wigan Athletic over Fulham. Both clubs had 87 points with Wigan’s goal difference being +33 (84 for, 51 against) and Fulham’s being +34 (72 for, 38 against). Without that change to ‘goals scored’ Fulham would have been Champions in a previous season. Both teams were promoted, however the experiment only lasted for three seasons before reverting back to ‘goal difference’.
After scouting the league tables back to 1888 l can now confirm that the Second Division in 1926/27 is the only occasion in all the Divisions when ‘goal average’ would have given a different outcome to ‘goal difference’ in determining promotion, although it’s not clear whether that would extend to determining relegation.