I don't think they are going strictly by 2nd AOR date, it seems to be random. I remember someone from Jan 2011 (2nd AOR) also went into process recently.
What is also unclear is why NDVO is the only one holding back MI-1s, see this link - buffalo 4131 MI-1 got medicals. If they are planning to eliminate all unwanted NOCs then why are other visa offices processing these, Manila is issuing visas for 0213, 4131 ...
http://www.canadavisa.com/canada-immigration-discussion-board/june-applicant-2010-t43317.0.html;msg1408554#msg1408554