I think the biggest problem has been changes to the Tenant Occupancy Methodology.
Notice I said Completions, not Approvals. In FY2012, the average I-526 monthly Completions were 386. For FY2013 October-February the average is 358. Average I-526 Approvals have historically been about 80% of Completions.
All the data is available in the
USCIS Dashboard.
Usually USCIS have also published the
All Form Types Performance Data on a quarterly basis which had the Approval figures, but they have not done so this FY. The last one available covers FY2012.