What is a 13 state warrant?

No idea, warrants are put on NCIC and will go to every state and every police agency that has access.

How is it being used

When I was a probation officer in Maryland I learned that there are various types of warrants that are issued depending on the seriousness of the offense. For the most serious offenses, the state police send two troopers all the way across the country on a commercial plane to get a person being held by another state on that warrant. In other lesser cases, they will only go and get their man based upon a lesser state radius. I don't remember exactly what these various types of warrants are called, but I assume that is what you are talking about.

If a police agency takes someone into custody based upon a computer check that reveals an open warrant in another state, and the state that has him is outside the warrant radius, the person is let go. In other words, they are not going to hold someone on another state's warrant if that state is not willing to come and get him.