The articles are from 1996 - 1997.
According to the appendix (1), this content was posted to Blues News in 2000.
First article: Quake's Game Engine: The Big Picture - Dr. Dobbs Sourcebook, Sprint 1997, #279, pp. 58-60. Last article: Inside Quake: Visible-Surface Determination - Dr. Dobb's Sourcebook, Jan/Feb 1996, #255, pp. 41-45.