REST API to get usernames within each Application

I can run the ‘/rest/api/2/applicationrole’ REST call and get a count of how many licenses are used in each application. This is working fine. I want to take it a little further and identify the people using the licenses. Is it possible to use the “Default Group” concept, can i rely on all users HAVING to be in the default group?

Example below, i can get the usercounts in the groups with applicationrole, could i think run a 2nd REST call to /rest/api/3/group/member and assume that each Active member in the group then represents the users consuming a license. Or can you consume a license but NOT be in the default group?

"name": "Jira Software",
"defaultGroups": [
"defaultGroupsDetails": [
"name": "jira-software-users-carlman1",
"groupId": "2c2e0eeb-0f68-4084-8d1b-a4eb7a430112",
"self": ""
"selectedByDefault": false,
"defined": true,
"numberOfSeats": 35000,
"remainingSeats": 34997,
"userCount": 3,
"userCountDescription": "users",
"hasUnlimitedSeats": false,
"platform": false