Why are the users that I want not listed in this table?

A user can be a member of up to 64 groups, and must have the same registry type as the groups that it is assigned to.

If a user that you want to add to the group is not listed, it does not have the same registry type assigned as the security group, or it already belongs to 64 groups, or it does not exist.

To create a user, see the Creating a User topic in the AIX® Information Center.