Irrespective of what is printed on the artistic work, the copyright is automatic (from 1976 onward) and belongs to the author(s) or their heirs. If there is a question of ownership, a court would need to decide.
Organizations own work-for-hire, and to establish ownership, you would need to prove the non-existence of the organization (reverting the copyright to the author/heirs) or determine the beneficiaries of a possibly ephemeral organization.
