I don't think that "Torrent Company" has any meaning to Filoni or Lucas. Every kind of promotional material related to Rex that I have seen have him referred to as leader of the 501st. For instance, both Cartoon Network's website and Starwars.com credit him as being in command of the 501st battalion. The EU seemed to make efforts to make sense of the fact as to why Rex is only a Captain while all of his peers are "Commanders," but even then that explanation put Appo as Rex's superior only for Umbara to show that isn't true. My personal guess (not confirmed to my knowledge) was that since Rex was going to be something of a main character along with Ahsoka (who is a commander), that maybe Lucas and Filoni made Rex a Captain so that it would be clear who is being referenced as commander and who is captain and show definitively that Ahsoka is Rex's superior, not his peer. *** Edit: Also on the topic of why Rex is a captain instead of a commander, if you go to his bio at starwars.com, but then click on Ahsoka's profile under the "relationships" heading, the first sentence is that she holds the rank of commander. So perhaps because Anakin has a padawan that supercedes Rex and holds the rank of commander, that might be why Rex is "demoted" in relation to Cody (since Obi-Wan doesn't have a padawan). Appo's ascension to the rank of commander might mean that both Rex and Ahsoka are out of the way at that point. *** However, in the real world "commander" is usually just a generic term to refer to the commanding officer of a particular unit, and the actual rank is usually associated with navies, not armies. It's not clear what the intent is on film, though the EU seemed to run with the idea of "commander" as a rank. For all I know, Cody is a captain too or a colonel or a major, etc. but is just referred to more generically as a commander because he's in charge.