The XX concurent users only comes into play if the licensed application offers such a thing. In the case of something like Office 2013, you'd definitely need 300 license...
But for Something like... Raiser's Edge, or a Student Information System... You'd only need to license for the expected number of concurrent users.
IE: Raiser's Edge can be installed on every computer on my campus... But only 15 of us can log in at one time.