When making a copy of the league for next season, the Final Average that is copied into the Book Average for the next season may be incorrect.
This problem may occur if the last week of the league is configured as a Fun Night or 'Roll-Off, Scores don't count'. The 'Make Copy' feature will use these scores for the Final Average even though they do not count, thus resulting in an incorrect Book Average for next season.
To workaround this issue, go to the last week where scores DO count. Then you can make the copy of your league for next season and will have the correct Book Averages.
Note: If averages are turned into the local association before the season ends, then you would want to go to the week where the Final Average report was generated from. Typically, this problem would occur if the Association wants the Final Averages by mid-April, but the league does not end until May.