Except as otherwise provided in section 16 of this act, [FN1] a court of this State may not modify a child custody determination made by a court of another state unless a court of this State has jurisdiction to make an initial determination under paragraph (1) or (2) of subsection a. of section 13 of this act [FN2] and:
a. the court of the other state determines it no longer has exclusive, continuing jurisdiction under section 14 of this act [FN3] or that a court of this State would be a more convenient forum under section 19 of this act; [FN4] or
b. a court of this State or a court of the other state determines that the child, the child’s parents, and any person acting as a parent do not presently reside in the other state.