The Total Amount of Option ARMs and Alt-As

In this interview with William Black, he tells them that the total amount of foreclosures that will occur will be a lot more than what the government and banks are saying will occur:

The professor and former financial regulator foresees another wave of foreclosures and future bank losses of more than $2.5 trillion vs. the government's $599 billion estimate.

In the 60 Minutes video on the right, Whitney Tilson says about $1 trillion in Alt-As and $500 billion in Option ARMs. If the government "tested" the banks on the assumption of a much lower total amount of Option ARMs and Alt-As than what's actually out there, then how reliable can this stress test be?