Your guess is 1/2 right. All of the errata from Professional ASP.NET 3.5 posted through the end of 2008
were corrected in the SP1 book.
The errata in early 2009 are probably also corrected in the SP1 book as we found some of those in the process of editing the SP1 book, corrected them, and posted them back. There may be a handful of errors from the 3.5 book that were found in late 2009 that still exist in the SP1 book as well.