I beleive you have to go back in and add the new balloon, it has been a while since i did full designs with assemblies and balloons. Changes after ballooning are not fully updated automatically unless it has been added in recent SW Editions.
As I recall, certain changes can also damage your relationships of your ballons and turn them yellow/gold. I suggest you always review your assemblies after changes and expect touchups to be required.
I've had cases where balloons didn't update until I clicked on them, but I believe this has gotten better with later releases.
As far as I know new balloons for added parts do not appear automatically also if they were originally inserted automatically. You have to do it manually.
Alternatively you can click the ballooned view and Auto Balloon it again, this will however change the pointers and balloons position.