I did perform your analysis for Nov. 2010, I got 6529. Assuming that the only increase in Nov 2011 was EB2IC and other other EB category filings were the same - a big assumption,
We get 7551 - 6529 = 1022. That is indeed a very low number.
other approach:
TSC + NSC Nov. 2010 = 17417
TSC + NSC Nov. 2011 = 20975
Increase = 3558 ...attributed all to EB2IC filings