1 Start Center template can be assigned to 1 Security Group. Each user may have multiple Security Groups assigned, giving them multiple Start Centers. The key to Result Sets is the use of substitution variables in queries for things like siteid, current date, ownership/responsibility, logged in user, etc., in building the queries, so that the result set will work for the user when applicable. Take a look at this
post on Start Center Design Basics - Roles & Performance that has a video link as well as additional documentation, including query segment examples leveraging substitution variables.