We were hoping to write an article on the subject but ran out of time unfortunately.
The just of it is comparing these two queries:
D and month<=8 and season
D and month=9 and season
Of the 11 seasons in the database, the three where dogs did the worst through August (2008, 2010 and 2011) all saw those seasons turn profits playing on dogs in September.
Just something to watch if bettors start shifting too heavily to favorites late in the season.