I don't think you have a messed up suspension, the screw will turn more than 18 out of the fork. when it is in the fork movement is relative to the rod down the center of the damping shaft. It sounds to me line the jam nut is not in the right position, there is a guide that has an o ring on the bottom of it, if that is to thick or the the nut is not down snug it will give more clearance at the top of the shaft allowing the screw to move more. Also there shaft down the center of the damping rod, thats what make contact with the rebound adjuster