A post from trackitt.com explaining possible reason

The moment someone enters the I485 club, it is clear that his PD is "current" as of that day, and that is why he/she was in the club. But between that time and the case coming to adjudication, if the visa number is not available (not as per PD, but just the availability of visa number from DOS), then such cases will be stacked in a separate shelf sorted by the PD. These cases will be reviewed periodically (monthly) and approved. So, I still hold the point that PD is not considered for adjudication, only visa availability from DOS at that instance of time.

--- 總結一下是說排期隻是個對供與求的估計，排期到了不一定有號兒（特別是現在財年馬上就要結束，中印這樣僧多粥少的國家號兒已經沒了），不current不一定沒號（特別是那些僧少粥多的國家）。批不批關鍵是有沒有號兒，而不是排期，特指對現在財年最後一個月，有號兒不用肯定作廢，不用省著以防PD早的NC突然在這最後一分鍾過了給耽誤了。

我覺得少數本月批了的幸運兒們是用了海外領事館事先申請沒用完返還的號兒。如果我的估計沒錯兒，下個月新財年開始，批準會多起來。

個人觀點，歡迎討論。