Several years ago, before the publication of the first Complete C&H collection, I found a web page listing all of the 17 other books listed in this wiki (or 18 if you include Teaching) plus at least one other, of which I can now not find any mention.
This missing book was rare even then, possibly unauthorized. I believe it was published in the UK. Similar to the familiar "Collections" titles, this book featured daily and Sunday strips. Unique to this lost book, however, was that the daily strips were expertly colorized so that the entire book had the same look throughout.