Disney has actually intended from the start of backstage to have the 4 Cog HQs. They just refer to it as "Cog HQ" because that was the name of the project in whole. Proof of this is back to the new map that came after the Sticky Note one. There were the 4 corners with dark grey smudges. (and there were the Under Construction signs)
The Backstage tells of things like Skelecogs patrolling the streets meaning the areas are protected. And how that was going to work was still in development. Most that you can find in the backstage is the basic idea behind each HQ. They are neighborhoods (look at the scenery, it looks like New York without all the fancy lights lol)
The reason for the unused music pieces is that it was replaced by newer ones. And a probable reason for the misleading names is that they are probably the exact same textures, models, etc. used as "sketches" for Cog HQ, as a whole, during it's development. To change it would mean to rewrite the entire coding for the game
The foot and camera you refer to have the Sellbot logo(either that or it's cingular) on them if you look close enough. They may have been an abandoned(or not yet implanted) idea of catching toons in the Boss rooms.