Personally, I'd never send anyone to Ken Russell's site for real information. I just read through his Leica stuff and it's just laughably ridiculous.
I've scanned about a dozen websites purporting to inform people about Leica gear. Most are poor, or full of personal opinions. Erwin Puts' online reviews of Leica lenses are often impenetrable. Clowns like Ken Russell make it a mockery. It's sad.
Leica has been around in 35mm format (arguably was the inventor of 35mm format!) the longest and has a rich history in both camera and lens design. There are many excellent books available on Leica camera and lens history ...
I don't presume to know the most accurate, the most readable, or the best fit to emr's interest, but I'd strongly recommend a visit to a the local library or to Amazon.com. On Amazon.com, do a search on "Leica camera history book" ... you'll get a couple of dozen potentials to read and learn.
Of the online sources, the one I respect the most is Steve Gandy's from CameraQuest.com:
http://www.cameraquest.com/mlenses.htm
Steve is a true enthusiast and makes no bones about his discussion being definitive or summarily accurate. He loves the gear, and says right up front in bold letters,
"This is a is a VERY opinionated USER'S and Identification Guide to Leica M Lenses. For any opinion expressed here, you can undoubtedly find someone with the opposite view. Discussed are most cosmetic versions, changes in optical formula, and the general reputed optical performances. This is a GUIDE to help you find your OWN way in Leicadom, not a map to tell you where to go. "Per van Hasbroeck" refers to Paul-Henry van Hasbroeck's superb book Leica, A History Illustrating Every Model and Accessory. If you read EVERY Leica book, you soon learn that experts often disagree. Some say a particular lens was redesigned, another maintains it was not. The strangest thing is that anyone gives a damn. Welcome to the wonderful, wacky, strange world of Leica nuts. ..."
I've known Steve for years, he's a straight shooter. I've got that book (published in 1984 so it's missing the last 27 years of Leica history ...) and it is indeed excellent. It is at least a good starting point to learn about Leica camera equipment ...
Have fun learning about the world of Leica cameras ... !