So both this one and Babysitter's Club are, technically speaking, disqualified by the prequel/sequel novels that you mention here. I'd consider making an exception for Babysitter's Club, since the novel is just a few months over the 12/31/09 cut off date, and it also is just one novel. But the Sweet Valley books were still being written by its original author, following the original two characters, all the way up until 2012. Can you explain a bit more as to why you think they should be considered as a separate canon?