Sources from a variety of dates might be useful. You could use an older source for context, history, or background on topic, then check newer sources for updated information or new developments.
Websites will often display a current copyright date for the entire site. This does not mean that all of the information on the website is up to date, especially for a large website which contains many pages and articles. See if you can find a specific date for the page or article you are using. You might also see and "updated" or "revised" date.
History: In some cases you will want to use primary sources that were generated during or shortly after an historical event. Newer sources may have uncovered new information about history, but often they draw on earlier resources.
Medical & Nursing Information: It is especially important that medical information be up to date. Generally, older than 5 years is considered out of date for clinical use, especially in nursing. Reputable health information websites will often show the date when the information was last medically reviewed.
Statistics: Don't expect up-to-the-minute statistics for everything! It takes time to compile and publish them. Keep in mind that sometimes the information is published long after it is collected.
