In fact, someone show me where it is conclusively established that there are four or five decks along the saucer rim. 'Cause I don't think it ever was.
Look at the airlock on the neck-pylon, the door is at least as high as the windows on the neck, which in turn are at least as high as the larger windows you can see here on the saucer.
It's reasonable to assume that the saucer can be, at the rim, as high as five standard-height decks.
Looking at this screengrab from the 2009 teaser where you can see a worker kneeling over to weld, it's EASILY five decks...