SKAdNetwork data is completely separate from any device-level attribution data collected via tracking links. With the expected low rate of ATT opt-in, SKAdNetwork will be the only reliable data source for billing, etc.
However, there are still advantages tracking links, including device-level attribution data (for opted-in users) and deferred deep linking (regardless of user opt-in status), and many ad networks are supporting both attribution methods in parallel.
This means that you will always get aggregate data via SKAdNetwork, and additionally receive device-level data via tracking links for the same user if they opt in. Unfortunately, due to Apple's intentional SKAdNetwork design limitations, there is no way to deduplicate these two data sources. This is why we expect SKAdNetwork will quickly become the standard option for transactional purposes like billing, with the limited amount of device-level data still being useful for deeper insights and campaign optimization.
Updated over 1 year ago