We've already identified the common contact which makes it obvious which is the common terminal. Now, notice that in the picture on the right the lever is clearly in the exact center (middle pickup) position. We notice that the wiper wedge is only touching one contact, that contact and its attached solder terminal must be the middle terminal for this pole. Now notice the picture on the left. The lever has been moved to the neck/middle position -- remember that we are looking at the switch from the back of the pickguard and the neck of the guitar would be to the right in this picture -- and the wiper wedge is now touching two contacts. We already know which one is the middle terminal, which means the other one must be the neck terminal for this pole. The only remaining unidentified terminal must be the bridge terminal for this pole.
The second pole, which is mostly hidden from view in the pictures above, is basically a mirror image of the first pole. I.e. if you flipped all the parts that make up pole A (wiper and insulator and the four contacts) and then rotated them about fifteen degrees (so the contacts are offset from those on pole A) you would have a pretty good idea of what pole B looks like. So, it should be real easy to figure out which terminals are which, right? Just reverse the order from pole A, right? No! It's a little more tricky than that. The common terminal is indeed where you might expect to find it. But, keep in mind that while the components for pole B are a mirror image of pole A they are attached to the same shaft and rotate the same direction. Therefore, the switched terminals for pole B must be in the same order as those for pole A. The terminal configuration isn't immediately intuitive for some people so I've provided the following picture that you can print to keep as a handy reference.
