But what about subsection B???

(b) If an order modifying or terminating a support order is entered due to the unemployment of either the support obligor or the support obligee, the order shall be made retroactive to the later of the date of the service on the opposing party of the notice of motion or order to show cause to modify or terminate or the date of unemployment, subject to the notice requirements of federal law (42 U.S.C. Sec. 666(a)(9)), unless the court finds good cause not to make the order retroactive and states its reasons on the record.

So this "earliest date" is NOT automatic, and... this is why people do need lawyers. I know I know. but... they often do.