In working on the manuscript, I'm running into a familiar problem, one I also encountered while writing the first book. The books contain, basically, information and plot summaries/critiques of historical novels published over a given time period. The primary market is libraries in North America; secondly, general readers, researchers, prospective historical novelists, etc.
I mention this because it's not practical for me to include historical novels in my book unless a significant number of libraries own them. I use WorldCat to determine this (link goes to the public version, which is kind of neat to search). WorldCat, if you're not familiar with it, is an online catalog of library holdings worldwide. The overwhelming majority of libraries in North America have their holdings - or those of a shared library system they belong to - reflected in WorldCat. To me, a "significant" number of holding libraries is usually around 50... if fewer than 50-odd libraries for any novel are recorded in WorldCat, it's not worth including it, because library patrons will get frustrated that the book's hard for them to obtain.
(Yes, I know interlibrary loan exists, and it's a wonderful thing, but not all patrons want to wait - plus, my book's not meant to be a comprehensive guide to all historical novels ever published, only representative ones. Anyway.)
The frustrating part, though, is when I read/come across novels that are truly wonderful, but which only a very small number of libraries own. These are mostly small press titles, ones that have word-of-mouth popularity on Amazon and on blogs. I'm sure you know some of them. I'd love to include them in the book and help spread the word, but I can't. It's a Catch-22 of sorts, because they're often not in libraries simply because they're small-press titles and missed getting picked up for review by the major trade pubs like LJ, Booklist, PW, etc.
This has me thinking about a few different but related things. First, I wonder if many authors consider libraries as a market worth pursuing at all, because in some cases, these novels aren't even owned by libraries in the authors' home states/cities/towns. Many libraries will acquire novels by local authors even if there hasn't been significant (or any) review coverage. So why aren't those copies there?
On the other hand, because a lot of these smaller-press novels are word-of-mouth hits, I wonder if libraries need to make more determined efforts to acquire them, rather than simply relying on the traditional review venues. If you're a librarian reading this, do you ever purchase historical novels based on blog mentions, online reviews, Amazon recommendations, etc., or do you wait for a formal review to appear?
It seems to me there ought to be a way for these two solutions to meet in the middle. Not just for the very narrow purpose of my being able to include them in the book, of course, but so that these novels can be acquired by more libraries, and therefore reach more readers.