Unfortunately, You can't learn much from reading a plug with multiple tunes and multiple passes on it.

Buy yourself a bunch of plugs from rockauto.com (very cheap NGK prices!), and make one pass. Click the car off at the finish line, take the plugs out, and cut one apart to see the fuel ring down at the base of the porcelain.

Driving it back, or multiple passes will give you bad information, and could just lead you in the wrong direction.