The rumormill has told me that these books, "Advanced Scholar 15" (or something along those lines, search the broker for "15") were added after the other low-medium level Advanced Scholar books. I can absolutely assure you however, that these books do now exist. I have a level 27 Sage, and I have every craftable Adept 3 spell in my recipe book (I even have my future books lined up in my bank through level 34). I also currently have an extra one of these books that I am holding on to for my Alchemist alt.