Had a quick look through the discussions, didn't see the reasoning for it, but, why are S16 and S23 not numbers? They're named?

Also I saw why Shada wasn't listed as a special episode, because was straight to DVD, but since was written as episodes, and S17 mentions them in the season blurb, shouldn't they be in the specials list? Like for example, Smallville... the unaired pilot is under specials, and name says it all, it was unaired so woulda also been right to DVD.

More curious about the 2 seasons with titles rather than numbers though. Thanks