AAAs still Junk -- in 2013!

Breaking news: Several securities, boasting ratings higher than France and Britain as of two weeks ago, are now thought quite likely to default.

Moody's changed its opinion on a number of residential mortgage-backed securities (RMBS), with about 13 of them being downgraded from Aaa to Caa1.

The explanation provided: "Today's rating action concludes the review actions announced in March 2013 relating to the existence of errors in the Structured Finance Workstation (SFW) cash flow models used in rating these transactions. The rating action also reflects recent performance of the underlying pools and Moody's updated expected losses on the pools."

In short: the model was wrong - oops!  ($1.5bn, yes that's billion, in securities were affected by the announced ratings change, with the vast majority being downgraded.)

Okay, so everybody gets it wrong some time or other.  What's the big deal?  The answer is there's no big deal.  You probably won't hear a squirmish about this - nothing in the papers.  Life will go on.  The collection of annual monitoring fees on the deal will continue unabated and no previously undeserved fees will be returned. Some investors may be a little annoyed at the sudden, shock movement, but so what, right?  They should have modeled this anyway, they might be told, and should not be relying on the rating.  (But why are they paying, out of the deal's proceeds, for rating agencies to monitor the deals' ratings?)

What is almost interesting (again no big deal) is that these erroneously modeled deals were rated between 2004 and 2007.  So roughly six or more years ago.  And for the most part, if not always, their rating has been verified or revisited at several junctures since the initial "mis-modeled" rating was provided.  How does that happen without the model being validated?

A little more interesting is that in many or most cases, Fitch and S&P had already downgraded these same securities to CCC or even C levels, years ago!  So the warning was out there.  One rating agency says triple A; the other(s) have it deep in "junk" territory.  Worth checking the model?  Sadly not - it's probably not "worth" checking.  This, finally, is our point: absent a reputational model to differentiate among the players in the ratings oligopoly, the existing raters have no incentive to check their work. There's no "payment" for checking, or for being accurate.

Rather, it pays to leave the skeletons buried for as long as possible.

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For more on rating agencies disagreeing on credit ratings by wide differentials, click here.
For more on model risk or model error, click here.

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Snapshot of certain affected securities (data from Bloomberg)