Although almost everything online is in constant revision (much to the consternation of some), you should endeavor to inform readers of the state of your document, especially if you know change is in the air. There are many "Under Construction" images that let people know you're still working on the document, or on certain sections of a document.
Old information is sometimes more harmful than none at all. If you place information on the web be sure you have a way (and a person) to update it.Be sure to time stamp your document so that people have an idea of when it was created and/or last updated.
In general, use a link to refer to information that you believe should be mentioned, but that you have no power to update. This way you always get the most up-to-date information from that source.Copy information (text or images) only when it's legal (and then with appropriate attribution), and when it's not likely it will change without your knowledge or ability to update quickly.