Welcome to the craziness. We know that the catalog numbers came out around 1924. So with that, you would think that popular items would have the catalog numbers around then. But the red book shows is the smooth bottoms came out around 1935. So why does the skillet still have a number on the bottom and not the catalog number? I honestly can't answer that, but I'm going to guess that the skillet is around 100 years old. And the one with the catalog number, is newer, but by how much? To go back in time would be amazing to catalog when things changed. I hope others can chime in and give you a better answer.