If a user applies for the same collection for the same partner a second (or more) times, it shouldn't go straight through as a fresh application. This should only be the case if their other application has not been Accepted/Declined/Sent.

They could receive a message saying 'You already have an application open' with a link and then have to confirm they want to apply again. The only time I can think that a 2nd application would be necessary is for partners where users need to request individual resources, and thus might put in multiple applications.