The Engineering Sample game pictured in this listing has no serial number on the cabinet. Cabinets used at the engineering stage are typically ones available from preceding production runs and the artwork would easily show this. However, we could not identify an earlier game having this Sample cabinet artwork. Instead, we found a game, Williams' 1969 'Expo', made a few months after 'Smart Set' that had this cabinet art design but with different colors. The Sample playfield uses a pink color in the outlanes and in the area of the arrow inserts, as well as inside the helm (ship's steering wheel). This pink color was changed to red sometime during production. The wheel spokes (inside the circle) were drawn as if the outer half of each is made of wood and the inner half is a black line. Sometime during production, all the spokes were changed to be entirely black lines. The game shown in the manufacturer's flyer also shows the pink color and wood spokes. This game shows the cabinet production colors, and the lower cabinet shows the green wave is above the blue wave. In all production games that we have seen, the blue and green colors are reversed in the lower cabinet from what is shown in this flyer. Also pictured here is an example located in South Africa that we have marked as Later Production by virtue of its higher serial number 50774. The playfield pink has been replaced with red and the wheel spokes are fully black. Its lower cabinet colors are reversed from the flyer. The backbox stepper unit inexplicably does not have its bell and clapper. However, the notable difference is that its two bottom standup targets are marked 'Down Post' while the two middle targets are marked 'Up Post'. This is opposite of all other examples shown here. We have seen only one other Smart Set having this target arrangement for its Up-Post feature. This arrangement is not supported by the game manual or by the schematic that we have in this listing. If anyone has a manual or a schematic that supports this arrangement, please contact us.