So much for the significantly better performance of the November and December 2007 loans (made with the bidding guidance) -- to my eye, the slope of those lines (since March 1) now appears to be the same as the July-October loans.
Yeah, they were doing good while people were getting their tax refunds back, but not anymore.
I don't think the timing is right for that explanation. The November/December loans were doing well for their first few payments, which were in December-February. Certainly there were no tax refunds in December, and I doubt there were a whole lot in January either. While some people could have e-filed in early-January (even before getting a W-2 or any 1099's) and gotten a RAL, I don't think that is especially common (but maybe it is more common for potential deadbeats than for more economically stable folks).
ETA: Also, people whose loans originated earlier are also just as likely to have gotten their tax refunds. So the "tax refund effect" should have lowered the slope of all the late loan curves, not just the most recently originated loans.