It's clear - RATINGS did not change upon Bear's or Lehman's AAA holdings - rather...

When Bear Stearns and when Lehman's customers, clearing banks and counterparties - walked away -
it was NOT due to a change in the AAA ratings of their holdings -
there was NO such ratings agency change -
the KNOWN and widely held belief that AAA securities ratings were one thing -
NOT TO BE RELIED UPON OR TRUSTED - in so far as as far back as 2007 the ratings agencies began holding meetings with CSE's on exactly that topic.

When the CSE's in part engaged in IBGYBG (I'll be gone, you'll be gone) behaviors with ratings agencies - WHEN - INITIAL RATINGS WERE ASSIGNED - it's as if tainted beef was not only snuck into the market - it was created, it was discussed, it was negotiated by and between the issuers, and close if not the same controlled underwriters then sold with AAA ratings that were known to be less than what customers / buyers were likely led to believe; subject to proof.

Again ending the siesta on the US Taxpayer's dime one little, easy to read blog at a time.