Erwin Puts has resolved his rights issue now with bankrupt Hove Publishing and now has it up as a free download. It has been out of print for several years and selling for over a 100 dollars on the used market.
This covers all Leica lenses up to the late '90.
If you are looking at used Leica lenses, this is a must have work. It also has production data which will allow you to date the production of it.
Free Download of Leica Lens Compendium