Rating agencies like S&P don't buy anything and their ratings have almost nothing to do with checking underlying data on securities.  They just set the odds based on reported information.  Institutional investors, on the other hand, should have the capability of analyzing the data before they buy anything, and most did.  But it still didn't save them from getting burned because lack of data wasn't the problem.  It was their beliefs and models about how the world worked that were wrong.