According to the latest SKAdNetwork v2.2 update on 2/1/2021, SKAdNetwork now includes View Through Attribution and has added documentation of the different types of attribution windows.
There are 2 different types of ad touch points, that are prioritized similar to how mobile attribution works today using the fidelity-type value that is part of the signature and the values passed to Apple upon the ad engagement. The value will later be used to define which engagement takes precedence.
The newly supported custom View-Through Ad which opens a 24h attribution window for the user to install the app.
This engagement has the lowest priority with fidelity-type set to 0.
A StoreKit-Rendered Ad which opens a 30 day attribution window for the user to install the app.
This engagement has the highest priority with fidelity-type set to 1.
As part of the SKAdNetwork postback the newly added fidelity-type value essentially will disclose the match type which is the most recent, strongest ad touch point within the attribution window.
A few more things to note:
To help ensure it’s a valid impression, StoreKit only records the impression if the ad was displayed a minimum of 3 seconds.
StoreKit records a maximum of 15 view-through ad impressions per source app before discarding the oldest one. The recorded ad impressions may advertise various products, and are each eligible to become pending attributions until they expire (after 24 hours).
After a user installs the app, there's a 60 day window for the app to be launched in order for it to be attributed to the original source (regardless of type of ad touch point).
In theory, though an edge case, an SKAdNetwork postback can be sent 154 days after an ad engagement (StoreKit rendered ad --> 30 days --> insatll --> 60 days --> 1st Launch --> 64 days --> SKAdNetwork Postback (assuming conversion value is incrementally updated every 23 hours, 59 minutes, 59 seconds.
According to this thread on the Apple Developer forum, SKAdNetwork will attribute an install so long as the first open happens within 60 days of the install:
