This summary is not the rule. The rule text controls.
If someone who shouldn't be part of a lawsuit gets added in, that mistake alone won't get the case thrown out. Courts have the power to fix these kinds of problems as the case moves forward.
A judge can add or remove people from a case at any point, either because someone asks or on the judge's own decision. The judge just has to make sure it's done fairly. This gives courts flexibility to correct who's involved in a lawsuit without having to start the whole case over.
The rule also lets a judge split off a specific claim against one party and handle it as its own separate case. This can be useful when one part of a lawsuit needs to move at a different pace or needs separate attention from the rest of the case.
