I wanted to add users to Creators and Administrators group. However, Windchill has deliberately limited the search for users to the top-level organization. I've multiple organizations' within one top level organization. They can be searched using Principal Administrators, but not within Creators and Administrators section for an Organization.
This is, I believe, a requirement for many big firms who deals with users from multiple organization. There're couple of calls associated to the SPR 2069096
Please vote so that there can be an added configuration to modify the search criteria for different groups such as Creators or Administrators.