The models are effectively identical, until they're not. In particular, they're not identical for the purposes of this discussion.
"Until pressure from a ceiling is applied" is the difference between stabilizing at 9 billion people (a bit more crowded than right now), and growing to so many billions or trillions that the grandparent poster's "no more toilets" prediction would be realistic.
"Until pressure from a ceiling is applied" is the difference between stabilizing at 9 billion people (a bit more crowded than right now), and growing to so many billions or trillions that the grandparent poster's "no more toilets" prediction would be realistic.