An IP "license" means the right to use the IP (and perhaps to copy, modify, and do certain other things to it as well). That right can be limited or unlimited, exclusive or nonexclusive, perpetual or for a finite duration, etc. "Assignment" means a transfer of the ownership of the IP--that is, a transfer of allIP rights.
The basic rule is that a supplier that creates IP owns it unless and until it assigns the IP to someone else. Possessing a copy of the IP is not the same thing as owning the IP itself. When a supplier licenses or provides a deliverable to the Commonwealth that does not mean that the Commonwealth owns the IP embodied in that deliverable.