Chat User : Hi, Muthyji. What is the priority date for a case using substitute labor? Is it the priority date of the original labor or the date of the I-140?
Attorney Murthy : Although, generally by law, the USCIS is supposed to give the date of the new I-140 filing, we have seen that they have been granting the PD from the original LC given for an earlier employee. So, although it may be possible to take advantage, the USCIS position is that their error does not guarantee the new substituted person may take advantage of something not allowed under law. So be prepared, even if the case has been filed, that it may not get approved if the USCIS realizes its error!
http://www.murthy.com/print/chat1213_P.html