The Vehicle Commander and Gunner are what counts for the qualification. They qualification is good for 9 months. If the TC or gunner have both qualified within the past 9 months, but on different crews then they are now a turbulent crew. Green, Yellow, Red is the easiest way to view. Green is they are in tolerance and qualified together. Yellow is they are in tolerance, but qualified within different crews (at that respective position so if a gunner becomes a TC he is not qualified as a TC) and RED is anything else.

A gunnery is just a qualification. So if someone asks why does a BSB do a gunnery, just respond with why do your Soldiers go the M4 or M9 range? A gunnery just proves that your crews are able to safely and effectively engage and destroy targets. My Supply Sergeant and his clerk have a 50 cal on their LMTV. I would prefer to know that they can safely employ that weapon from that platform if called upon.