Fork blades, and seat and chain stays are not typically butted. Many years ago Reynolds patented "taper guage" fork blades, which meant that the round tube used to create the blade was butted with a long, gradual decrease in wall thickness so that when the dropout end of the tube was tapered from 22mm diameter to 12mm diameter the wall thickness would end up uniform from end to end. That patent has long since expired, and this process was in common use among all manufacturers by the 1970s. Chainstays and seatstays were not given this treatment, and you can easily see that the dropout end of these stays is noticeably thicker than the other end.