My guess is the 1.7 TRILLION is the total of loans packaged and sold by WMB/WMI. The law stipulates that those who package and sell mprtgages must purchase at least four percent of the mortgages themselves. When you multiply ,04 times 1.7 TRILLION you come up with 628B. Rumor has it that WAMU purchased more than the four percent required by law. So, my guess is, the 635B is the value of the MBS owned by WAMU.
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