Just my guess but...
Effective May 1, 2002, bunch of other consulates (mainly those in Asia, Oceania) were added to the list of those who need to send the P3 to STL, not directly to the consulate. My concern/guess is that now so many people are going for this STL->NVC->consulate route, both STL and NVC are just swamped with all the P3, which might be causing the delay. Just a thought.
For more info on this change, please see the previous post by Moulin Rouge:
Moulin Rouge "March 140 Approvals track here.." 4/5/02 10:06am