Found this in GURPS Behind the Claw.
"The Glisten system has two huge asteroid belts, one ofwhich is designated the main world. In fact there are many settlements, each with its own ports. Most of the settlements specialize in a particular social or economic/industrial role. Glisten City is the main governmental and business district. The Pluvis group is the main shipbuilding center for the system, containing the vast Ling Standard Products and Bilstein shipyards and other, smaller yards of lesser importance."
Not sure how to interpret that though. It seems to say that each settlement has it's own port, but it doesn't clearly state if they are sub-ports of the Starport or Spaceports. Although it does say that the port for the Pluvis Group is the one with the shipyards. So, now I am kind of at a loss for what the writers intended. This does say that all of the shipyards are located in one port, which is rewritten by later books.
In the end, your universe, so it works how you want it to.