I agree with most of your points, mainly that marketing is coupled with other industries and it's probably why it's hard to measure its contribution to GDP.
I see the main point of our discussion is about the possibility of marketing continuously increase GDP. I can see it happening due to people forgetting about old products or maybe its features, and than you have the re-brand of the product or the re-make. Again, I'm not saying it happens exactly how I'm saying or that it represents a great part of GDP growth. But I'm saying that assuming constant/stagnant population growth and constant/…