I think you'd benefit from researching a bit more around what major brands do from a measurement standpoint. With the benefit of that much data, you can do some

I think you'd benefit from researching a bit more around what major brands do from a measurement standpoint. With the benefit of that much data, you can do some fairly accurate econometric/media mix modeling and get a solid read on lift for core metrics that they've invested a lot in to understand their impact on the bottom line. There is absolutely garbage inventory mixed in, and lots of solutions to try to minimize the impact of that, but to assume that these major brands don't know how this all works is naive. Further, just as an example, both Google and FB have very solid options for importing offline conversions which are relatively easy to map back to an audience ID of some sort.