Yes. I noticed the center of the wheel looks different than later years as it looks like it sticks out further by being more elongated / curved in the area where the slots are which makes them look larger when you look at them at a certain angle. The later years seem to have less curvature or a flatter profile. I always wondered why it looked different. Being an early one year only design would explain it. Maybe the later change was to allow for more backspacing without making the center cap stick out too far. I have read so far that the DG would be correct only on a 67 Chevelle or Camaro with disk brakes.

You have it exactly correct. 67 used DG for Camaro and Chevelle wheels only. The DG wheels are very hard to come by.