The Rules of the Game
I always thought that the "all rounds but the first require three references" rule held through the final rounds, and that each forward-pointing link that stops being required is thus replaced by an additional backward-pointing link. (So TUV requires links to written articles and one to a phantom, and WXYZ requires three links to written articles)
(Not that it's likely to matter in the current game; by that point most people are going to be more likely link-heavy than link-light…)