License count off by one

[Jonny Polivka]

Hello:

What uses a license in Bitbucket?

There are bitbucket_users, bitbucket_administrators and Bitbucket Internal Directory. 

On our system, if I add them all up, the value is one less than what is reported on Licensing page License Users field.  So if 90 users, 3 administrators and 3 Internal directory accounts, that's 96 but Licenses page reports 97 licensed users.  What would be occupying the one?

I should add Jira (v8.5.1) is being used for user management.

Thank you.