In the Sci-Fi double feature article you stated, “Actually, only 14 authors have had novels win both the Nebula and the Hugo, meaning that four sci-fi/fantasy scribes have pulled off the legendary awards two-step twice.” It does not to be four scribes that each received two doubles, it could have been three scribes with one having four doubles and two having two doubles each, two scribes each having four doubles, or one scribe with eight doubles.
