Seems to be as per this memo posted in the complaints thread
http://boards.immigration.com/showthread.php?s=&postid=762575#post762575
NSC Describes Its Plan for Concurrent Adjudications of I-140s/I-485s
Cite as "Posted on AILA InfoNet at Doc. No. 04042062 (Apr. 20, 2004) ."
CHANGES TO NSC PROCESSING OF I-140s/I-485s:
Effective April 1, 2004, the I-140 process was moved into the Residence Product Line. This was done to facilitate the concurrent adjudication of the I-140/I-485's, which will take effect April 30, 2004. This change is not part of the pilot program to adjudicate I-140/I-485 adjudication within 75 days of filing. EB stand-alone adjustments will continue to be processed, but it is anticipated that processing times will slow as the NSC works two tracks of EB adjustments.
NSC will soon be advancing the PTR dates for EB adjustments. Once less than 10% of a month's cases are still pending, the PTR date will advance to the next month. It should be noted that a small percentage of cases filed prior to the PTR date will still be pending. These are generally cases with expired prints, or more significantly, with pending FBI Name checks.
NSC is currently preparing all EB adjustments for adjudication which were filed December 2002 or earlier. Cases are deemed "adjudication ready" when fingerprints and the FBI name checks are completed. The NSC Contractor reviews all cases filed in December 2002 or earlier on a weekly basis to identify every case ready for adjudication, or conversely, every case with newly expired fingerprints requiring fingerprint rescheduling. This process ensures cases are brought to the adjudicators as quickly as possible and that older cases do not get overlooked.
Most cases filed prior to December 2001 which are not "adjudication ready" are held because of problems with the FBI name clearance. At the NSC there are approximately 2,200 cases filed prior to January 2002 which have not been cleared for adjudication. There are over 24,500 cases filed between February and December 2002 that are waiting for clearances. Again, the NSC sweeps "on deck" cases weekly to move the I-485s that have completed the mandated security clearances to adjudication