Autodesk recommends unassigning students at the end of every term or beginning of the next term to free up seats for other students
As an administrator of your Autodesk account you have access to usage analytics in Autodesk account which shows the number of seats remaining by product
For schools with SSO enabled If you reach the seat count for a product and a student tries to sign in and there are no entitlements available the student is redirected to the Education products page (US site) where they will be able to access and download products on their own