Clone Trooper ranking

This topic is sort of a continuation of what was being discussed in another thread - the wrong thread for the topic - regarding confusion in clone trooper rankings.

One question was why is Rex a Captain and not a Commander like the leaders of the other principle clone units we see (Bly, Cody, Gree, Ponds). My initial guess was that maybe Rex is just an exception in the same way that a Lieutenant can sometimes lead a Company even though Captains are usually the ones in charge. Starwars.com supports this as it says that he is "in charge of the famed 501st Clone Trooper Battalion." If that's the case then the 501st's highest ranking officer is Rex, a Captain while later it becomes Commander Appo a commander, which suggests to me that it's likely that Rex will die prior to ROTS (it seems odd that the highest ranking officer in the 501st would be both passed up for a promotion and replaced by Appo).

Wookieepedia's answer is that the 501st is an elite unit stationed on Coruscant that is deployed in smaller units as needed rather than the whole Legion being deployed. So, it claims that Torrent company (under the command of Captain Rex) was sent to serve under Anakin, whereas Obi-Wan, Aayla, Mace, and Luminara all have battalions (led by commanders) under their command. Commander Appo and the rest of the 501st would then still be back on Coruscant.

However, several things I noticed are that battalions we've seen thus far are usually color coded (Cody's is orange, Ponds' is maroon, Bly's is yellow, etc.) The color of the 501st is blue, and Rex does have blue markings, but the troops he leads do not which makes me think that, if he is just the leader of a company, his troops might be supplemented by non-501st troopers.. Also, in one of the new clips there is a bit in which Anakin says something to the effect of "how many troopers do we have" and Captain Rex says something like "I've managed to organize several brigades" (which are units even bigger than the battalions led by Clone Commanders. Which makes me guess that perhaps his standing in the 501st legion gives him special privileges over other clones, even if he is technically of lower rank (similar to how a Jedi commander has authority over a clone commander).

 

Interesting.

I wonder if the 501st tends to have higher rate of casualties, given that, if they're serving under Anakin, they're probably where the action is hottest.