Have you had the calipers off, and if you did is it even possible to get them mixed up? If they are reversed, then the bleeder valves may be at the bottom with the air at the top. Aside from that, it seems that the rest of the posts cover
everything else. Although you've done it a number of times, I will assume/suggest starting to bleed them with the right rear, then left rear, on to right and then left front, in that order. If you still consider or want to rule out the master cylinder, you could take the lines loose from it and use plugs to seal the master cylinder off and make sure the master isn't bleeding off.