From Muthy's website :
http://www.murthy.com/2012/05/23/pri...-do-they-work/
They can review a pending case at any time even if the Case is not current. But except RFE, NOID or Denied no other statuses are listed... hmm... this is really messed up...
The USCIS reviews I-485 applications even if the priority date is not current. If there are problems with the case, a request for evidence (RFE), notice of intent to deny (NOID), or a denial could be issued. If the case is proper and complete, the USCIS will place it on hold and, unless something changes for the worse in the case, it should be approved once a visa number becomes available.