Timeliness: When was the information published?
Most print information sources show a date of publication. After they have been published for the first time, some books are revised. When they are re-published they are called a new edition, or the 2nd edition. This is different from a reprint which just means that the same book has been printed again without changes to the content.
You may need to check the Library Catalogue to see if you have the most recent edition of a book.
Many web pages do not give a date. When a date is given, it is often difficult to determine whether it refers to when the information was first written, placed on the web, or last revised.
If a website has no information about when it was created and if it is updated, it may not be appropriate for academic studies.