> There was no way of rigorously testing whether individual customers propensity to purchase a good from a given business was actually tied to any of the brand

> There was no way of rigorously testing whether individual customers propensity to purchase a good from a given business was actually tied to any of the brand awareness ads that were being purchased This isn't right. Of course there was - statistics, sampling and A/B testing was invented way before computers or the Internet existed. Advertising is just applied sociology, and sociology is just statistics when done right.