If you delete a project without deleting the mappings the licenses are still used. This usually occurs when you are doing testing and need to re-use the licenses later on.
Waiting for a fix in a future release of NDS Migrator
If you delete the mappings and then delete the project the licenses are reclaimed but if you have already deleted the project the only way to get your licenses back is to use the DBInstaller to delete and re-create the database.
*WARNING* If you delete the database all existing Projects/Settings and Mappings will be gone.