As everyone, who listened to the recent "Goldman" enquiry, knows banks tend to offer depreciating positions in over-the counter (read "impossible-to-value") securities to more "naive" clients.
What is not common knowledge is in some cases they may be able to assign loosing positions to client portfolios retrospectively.
In sum, Michael Burry had his positions marked against him for over 2 years. So obviously joe mutual fund nor most hedgies could hold these CDS' which lost value each day until achieving their massive returns...