Cover and title page (and online searches) confirm correct spelling of this book is "Sea-Lavv" with 2 v's. However the site's font renders the v-v as a w anyway.
The Prisoner novels have been reprinted periodically. Does anyone know if #3 has ever been reprinted under the author's current name, Jean Stine? I don't know when she changed name; if it was within the last 20 years I don't know if there have been any reprints of it. The first book by Thomas Disch tends to be the one that gets reissued a lot.