You take a roster and can use all the players on that roster, but from any season in their career. Typically, any player listed as playing for the team on baseballreference.com is eligible, not just those with seasons in WIS.
So if you take the 1982 Yankees, Don Mattingly played for them, but not much. If you "twist" the '82 Yankees, you can use any season of Mattingly's career.