Source Citation Fail

While reading a technical book, I came across a footnote referencing a source citation with a Wikipedia URL. I frowned upon seeing an encyclopedia as a source. A book or article would be more useful to me. Ignoring the arguments about the quality of Wikipedia versus other encyclopedias, let's look at problems on how this turns into a source citation failure.

It turns out the specific URL has changed, and Wikipedia redirects to a the same topic on another page. However, there is no mention of the specific point referenced by the book as someone has since updated the entry. The page also boldly states at the top that the entry "needs attention from an expert on the subject."

The author of the book is an expert on this topic, but chooses to cite an encyclopedia entry in need of improvement, and the point in question has since been edited out. No value to the reader.

Please cite a solid source that provides more information to the reader.