It's my understanding that these are both predecessors of the ships we currently have. The B-Wing in the episode is openly acknowledged as the prototype. It doesn't even have a working hyperdrive yet. That's why the Attack Shuttle was docked to it when it jumped in -- they were using the Phantom's hyperdrive to get the B-Wing into the battle.Kind of stupid? I also hate how they're making the A-wing and B-wing older fighters, and not new designs.
It also makes sense. I mean, you have to start somewhere if you want to end up with the X-Wing and Y-Wing. They still need to show us the C-Wing through W-Wings.
I think it's been stated that the A-wings we are seeing are just part of a different Rebel cell; X-wings being in use by the particular cell that eventually assaults the Death Star. Yes, a bit of ret-conning but I like it.
I'll just say I LOVE the show and there's nothing wrong with disliking the show, and hopefully the thread won't dissolve into a flamewar.
Oh, don't get me wrong, I like the show, but they've done soo much crap with it that doesn't make sense. As for the whole rebel cells thing. The Rebels in Episode 4-6 are the Rebel Alliance. Emphasis on Alliance. All of them. And again, they're making out A-wings to be mass produced by the company that makes Star Destroyers. So many problems arise just from that, let alone appearing this early in the canon.