[avmich]

For every human onboard ISS there is always place in the docked spaceship. Exceptions: when spaceships break, replacements are usually sent - like, when Soyuz lost coolant or Starliner was considered too unreliable. While waiting for replacements, those ploblematic spacecrafts still serve as lifeboats, except maybe Crew Dragons can carry more people than those 4 they usually carry...

[KlutzySofa]

Crew Dragon can do 7 astronauts, but NASA only wanted SpaceX to build it for 4.

The contingency for the Starliner astronauts in case of an emergency was to strap them down in the cargo area. Which wouldnt be optimal, but better than certain/likely death onboard the ISS.