Looks like no-one is prepared to give you an answer on this.
Stock is a numbers game, as well images need to be pin sharp, have great colour and be of a subject that someone needs. Some libraries do not accept digital images less than 55Mb uncompressed (tiff) in size, as the quality is just not there. In my case, in Sydney, Australia, our harbour bridge makes a great subject, but there are thousands of images of it. If someone makes a request for a shot of it through a library, they are likely to get 100's of images. Yours has to stand out amongst those. A figure I heard a long time ago, was you make about $1 per image held at a library per year. Due to the proliferation of royalty free imagery, plus many more great photographers with fully auto cameras, I suspect this figure is now lower. Many stock shooters have reported a loss of business in the order of 80%. I actually run a stock library for another photographer, and I have also noticed requests way down on previous years. This library is a specialist library though, concentrating on ecological type images.