Given the timeline, I wouldn't be surprised if the Rebel Alliance as we saw it in the films didn't quite exist yet, and that any "Rebels" are simply independent groups doing their part to strike out against the Empire.
It's been said in interviews that the show is about the formation of the Alliance (as in, it won't even technically exist as a unified force in the first couple of seasons), so I think that's definitely set in stone - and why our heroes are a ragtag bunch instead of rank-and-file soldiers.
But speaking of rank-and-file, I'd love to see Kota's militia get fleshed out in there!