Even if both accounts are running the important feature is the "joining the Team effort we are looking for here" Form the Help and Support links on the DNet WebSite I found this:
Joining a team
"To join an exising team, you will need your stats password. To learn how to obtain your stats password, check out this section of the stats tutorial.
Once you have your stats password, you need to go to the stats page of the team you want to join. To join the team click on the "I want to join this team" link at the very bottom of the page. You will then be prompted for your email address and your stats password. Once you enter this information, you will be signed up under that team. Your subsequent work will be credited to that team from the next stats update on."