You want to choose the dates that will be included in the stats, you can do so by specifying the dates you want to be included. Anything in-between those dates will be calculated into the stats, anything outside of those dates won't be calculated in.
Go to Menu > Manage > Statistics/Standings > Stats/Standing Grouping.
Choose Teams or Players.
Select the league, Pencil to edit.
Advanced section, Start Date.
