Under the procedure established by RURESA, after a support order was registered for the purpose of enforcement it was treated as if it had originally been issued by the registering tribunal. Most States interpreted these registration provisions as also authorizing prospective "modification" of the registered order. However, except in circumstances in which both States had the same version of RURESA and the formalities were scrupulously followed, the registering tribunal did not have the legal authority to replace the original order with its own order. In short, most often the purported modification in essence established a new obligation. In sum, by its very terms RURESA contemplated, or even encouraged, the existence of multiple support orders, none of which were directly related to any of the others. Although the issuing tribunal under RURESA retained a version of continuing, exclusive jurisdiction to modify its own order, that power was not exclusive. The typical scenario of those days was that an obligee would seek assistance from a local court, which would determine a duty of support existed and forward a certificate and order and petition to a responding court. The subsequent proceeding in the responding State would bring the obligor before the court. The obligor typically sought modification of the support obligation (which almost always was not being paid) in a forum which presented him with the "hometown advantage." Thus arose the common practice of the issuance of a new, lower child-support order.

Under UIFSA, as long as the issuing State has continuing, exclusive jurisdiction over its child-support order, see Section 205(a), supra, a registering sister State is precluded from modifying that order. Without doubt, this is the most significant departure from the multiple-order system established by the prior Uniform Act. However, if the issuing State no longer has a sufficient interest in the modification of its order under the factual circumstances described in Section 205(b), supra, and restated in this section, after registration the responding State may assume the power to modify the controlling order.

Registration is subdivided into distinct categories: registration for enforcement, for modification, or both. UIFSA is based on recognizing the truism that when an out-of-state support order is registered, the rights and duties of the parties affected have been previously litigated. Because the obligor already has had a day before an appropriate tribunal, an enforcement remedy may be summarily invoked. On the other hand, modification of an existing order presupposes a change in the rights or duties of the parties. The requirements for modification of a child-support order are much more explicit under UIFSA, which allows a tribunal to modify an existing child-support order of another State only