alt Hacker NewsPartially, yes. Ads are also psychological, and tracked cross-platform. If you see a BMW ad on Facebook, drive by a BMW billboard on the highway, search BMW on Google, and then go buy a BMW, they have ways of fractionally allocating the conversion to the different impressions. It's pretty crazy.
I always thought last-click attribution was generally used even though partial attribution was technically possible. But my info is a few years stale.