Geoffrey Tweedale's Directory of Sheffield Manufacturers is indispensable, and easily the most accurate source of information about old Sheffield manufacturers out there -- it's not just razor manufacturers. It's not exhaustive -- the Print on Demand format has a maximum number of pages and he filled it -- but it's got 98% of what you're ever likely to find.
What it does not have is an extensive group of marks used on razors. ScienceGuy has a good collection of those online, however. You can find
them here, along with enough pictures of beautiful old razors to dehydrate you from drooling.
And putting together a book is on my long-term to-do list. ;)