Why do X Series VCC licenses show 0 assigned when there are users that have X Series VCC licenses assigned to them?

Each X Series VCC license provides 5 users (or VCC seats). The tracking is done by the Additional Named User license pool.

In the example above, this account has 10 X Series X8 VCC licenses, so 50 total VCC seats are allocated for the account. This is reflected in the Additional Named User license pool. There are currently 47 unassigned indicating that there are 3 X Series X8 VCC licenses assigned. The Unassigned number of X Series X8 VCC licenses will never get incremented, only the Additional Named User licenses.