Many subjects have multiple reference sources available, by different editors and publishers, varying by date, length, and, in some measure, viewpoint. For example, research on biblical interpretation is served by a variety of reference works, covering a variety of approaches to and historical contexts of biblical interpretation.

Several different reference sources are also available on Judaism, for example. Though the most recent and extensive scholarly resources on your subject are usually preferable to older and shorter/briefer resources, others may also be useful for you, depending on your subject and the nature of your research. In any case, consulting all that may be helpful is usually advisable, rather than limiting your reference work to one or two sources.