If you look through his earlier postings, he found some evidence suggesting WMI participation rate in the MBS WMB sold was between 25% and 50%. I think he took the 25% number and applied it to the total MBS sold by Wamu between 2000 and 2008 to arrive at the 172B. However, I believe you should probably discount the 172B by 25% to 50% because we dont know what the put back clauses are for the entire portfolio and many loans were probably refinanced during the last 10 years.
Interestingly, if you apply a 50% discount rate to the 172B you get 86B... which coincidentally is also the conservative amount Dr. A submitted in court years ago.
Additionally, when I went through the numbers on the last available Wamu 10K from 2007, I also came up with a theoretical $145B to the loan portfolio value..based on the reported interest margin on their entire portfolio in 2007. So I believe the max $172B and min $86B bound on the safe harbored loan portfolio is a pretty good estimate.
MAX $172B, Min $86B, IMO