Autodesk switched to user seat licenses in lieu of project licenses. Currently when you have 500 Field and 100 Glue and 25 Doc's Licenses there is no way to manage that license pool other then a bunch of e-mails between support and yourself. The only thing you can see in HQ and in the product silo's is users in the system or by project. When Autodesk switched to this revised licensing model they should have updated the administration head end to match and allow companies to manage.
In addition, you should be able to just disable users in field, glue, doc's -- in lieu of deleting them for a project. (just like buzzsaw is today).