As mentioned on the comments to the question, and as common sense indicates, having the published date on the page is very important.
But there are more dates or periods that you have to consider, for instance, date of references used, date of research if any, date of validity if it's possible to assess that aspect, etc. Any date that is relevant should be present on the content, either on a separate section dedicated to general information about the content or in the content itself. Of course footnotes and similar mechanics are good. All that is common practice in the printed world and you can see many references and dates used on books, for some reason, we don't see it that much on Internet; most probable for lack of experience on how to do it and/or laziness.
All that information help the user to recognize if the information is still valid or not. But of course, you can add a headline stating that the information is outdated and that they should go to a more recent version of the page/information and then you provide a link for it. If there is no more up to date information, then just mention that it is or may be outdated.
You also may use microdata, like RDFa, Schema.org or any other that you like to provide that information. Using microdata, may help search engines to inform the user and may be, in the future, used by tools on user agents to improve the user experience by informing the user about the state of the data/web site. The problem with microdata, right now, is that it doesn't offer attributes or properties to indicate the end of live of many things, although it does for some things, and there are mechanisms to extend the schema, plus slowly they add more elements, so at some point it will be available on common branches that don't have it right now.
So, I would add as much information as possible on the page and would use microdata with the available information and keep an eye on possible expansions of the microdata shemas.