So you're saying that all 4 should be the smaller knob style and that at some point the fronts got changed out?
I will say that the ones in front with larger knobs look to be in better shape. Possible they are in fact newer.
As to the spacers, MEK, there's definitely two different ones for front and back. I believe my fronts are the thicker ones... possible I got them mixed up at some point, though. :-)