Re: It's all about the forces involved
That heavily depends on the desires of other countries to mess with the situation. If say, someone in the U.S. establishes a colony somewhere and refuses to obey the treaty, and the U.S. wants to defend the treaty, all they have to do is prevent any supply launches until things change. Companies trying to launch from elsewhere will have trouble getting access to the launch capacity since existing launches would be going somewhere else and it's not easy to get emergency access to a launch facility with your own rocket. Only if existing governments wanted to provide that emergency access in order to annoy the U.S. would that change.
Once there is a lot more development where the colony is, that situation will be different. At that point though, there will be authority of some sort established there.