Yes, I've encountered this problem, but my main reason for writing reviews is to give myself feedback of what I gained from the book, and provide a mental path back to it.

source is unfortunately not available for me to contribute improvements myself

This is actually a business idea in my "potential todo" pile (some money can be made by referral links, at least enough to "support the habit"). I reserved a nice domain for it a while ago. Let me know if you (or anyone else here for that matter) have an interest in developing or writing for it. We can set up a scheme with x% of links going to SIAI.