 <p>I think a lot of the problem deals with the fact that search engines give something a high rank if a lot of people are linking to a specific page. Unless you can get all the people linking to your old documentation, to link to your new documentation, then you are going to have a problem with the older documents being rated artificially high. In order to overcome this, you might need to change the way you handle documentation pages. One good way would be to always show the newest information on a particular topic, and then only by clicking on a link on the page, do you get to the older versions. Optimally, this would be the same page, with a different parameter, to state which version you want to get documentation for.</p>