Previously we only took into account every survey ever filled in by a user, regardless of the date. Unfortunately this would mean that when people changed or left their teams, they would take the results with them. As a solution we have now historicised the results, so that you can have more reliable data about what happened in the past.
We now take into account the date when someone joins and leaves a team. This means that when a person joins a new team in May, we'll only return the results from surveys that person filled in starting from May. Likewise, for his/her old team, we'll only show the results of surveys filled in until the month of May.
With these changes, it makes more sense to compare team scores over a period of time.