The stage select text is positioned upwards, too, possibly because of the lack of slots like Final Zone. It's possible that Scrap Brain/Clock Work Act 3 had the boss fight in it, similar to the other Acts. Some acts have Xs listed after them (possibly to mark if they were incomplete), and Final Zone is missing from the list.
Later on, the palette got changed to the final's sepia-tone feel. The stage select once used a bluish-grey palette instead of a sepia-tone one. (Interestingly, this title screen heavily resembles the one from the 8-bit versions.) Since the title screen shares the same art/palettes as Green Hill, it used to have the differently detailed background in early pre-release materials before it got adjusted to resemble the final's background not too long afterwards. The title screen of the build shown at the Tokyo Toy Show has a smaller banner (and 'SONIC' text).
