(a) In a suit for modification or a motion for enforcement, the clerk shall file the petition or motion and all related papers under the same docket number as the prior proceeding without additional letters, digits, or special designations.
(b) If a suit requests the adoption of a child, the clerk shall file the suit and all other papers relating to the suit in a new file having a new docket number.

(c) In a suit to determine parentage under this title in which the court has rendered an order relating to an earlier born child of the same parents, the clerk shall file the suit and all other papers relating to the suit under the same docket number as the prior parentage action. For all other purposes, including the assessment of fees and other costs, the suit is a separate suit.