Level 27
Level 28
Level 37
Level 38
Level 47
Level 48
Level 50

Placeholder names for some levels that either weren't named or weren't updated at the time with their name. Level 27 and 28 are in Midday Gardens. Level 37 and 38 are for Evening Lake. Level 47, 48, and 50 are for Midnight Mountain. Here's my predictions for what they were for:
Level 27 - Spider Town(Sparx World)
Level 28 - Spike's Arena
Level 37 - Starfish Reef(Sparx World)
Level 38 - Scorch's Pit
Level 47 - Bugbot Factory(Sparx World)
Level 48 - Sorceress's Lair
Level 50 - Super Bonus Round
Those are based on what is missing in the list and the pattern...

Oddly, Cloud Spires is named Cloud City in this build.

Haunted Tombs is called Catacomb Caverns.

Dino Mines is called Dry Gulch.

The text "Guidebook" is in this build, and "Atlas" is nowhere to be found. This could mean the Atlas was still called the Guidebook in this build.

Grouped with the options are "HUB2HUB"(Yes, that's how it is), "Boss 2", "Boss 3", and "Boss 4". Possibly just placeholders to fix some sort of bug?

Although not used in game, this error message is amusing: "*bleep* *bleep* *bleep* *bleep* *bleep* - out of memory for book vram - %d bytes". These are bleeped by this site, but you could guess what it says. Here's a hint: F--k.

That's all I've found, but who knows. Maybe there's more.