Unless you count animation errors, nothing.
I thought I read somewhere that the episodes with Octane and Starscream's ghost were originally supposed to have Blitzwing in them, but they chose to have Octane, to sell his toy (that's why there was a cartoon, remember). I personally liked the episodes with Octane because they fit his personality. Had they done the Starscream Ghost with Blitzwing it would have been weird, plus why the hell would Blitzwing have been friends with Sandstorm? This was one other thing which made better sense in that episode. We don['t know those characters that well, but explaining their friendship (going back to Paradron?) is easier than showing Blitzwing to be a traitor.