Citation, Documentation of Sources

Q. Dear CMOS, I’m confused by the online encyclopedia entry examples in 14.234. Why does the Masolo example include an open date (1997–) while the Middleton does not? Many thanks for your help! 

A. The Masolo citation is of an online publication that began in 1997 and continues to be updated, whereas the Middleton citation is from a printed book that came out in 2004  (thus no updating). As a courtesy, the Middleton citation provides a link to the online version as well:

Masolo, Dismas. “African Sage Philosophy.” In Stanford Encyclopedia of Philosophy. Stanford University, 1997–. Article published February 14, 2006; last modified February 22, 2016.

Middleton, Richard. “Lennon, John Ono (1940–1980).” In Oxford Dictionary of National Biography. Oxford University Press, 2004; online ed., 2011.