(a) Except as necessary to comply with the requirements of section 4687 of this title, no insurer may agree with any other insurer or with an advisory or service organization to adhere to or use any rate or supplementary rate information. The fact that any insurer adheres to or uses such rate or material is not sufficient in itself to support a finding that an agreement to adhere or use exists but may be used for the purpose of supplementing any other evidence as to the existence of such an agreement.
(b) Two or more insurers having common ownership or operating in this State under common management or control may act in concert between or among themselves in the same manner as if they constituted a single insurer.