Thanks, that’s what I was thinking, that advertisers figured it out early on, and they aren’t smarter or dumber than the rest of the professional population, so this shouldn’t be some surprise that took years to work out.

(I personally remember thinking exactly that, that cookies allow universal tracking, as soon as I learned of the concept, but I don’t want to put too much stock into that belief because of the possibility of hindsight bias and misremembering.)