The date of the publication is important to determine how current is the information you have found. The date of the publication is important to determine how current is the information you have found.
Books take time to be written and compiled.
It is possible that a book with a 1998 publication date was completed and submitted for publication in the previous year. An article in a scholarly journal may have been submitted for publication a year or two prior to its actual publication. An article in a popular magazine may have been written the previous week.