"A first annual install may result from an app’s first-time install, a reinstall, or an update from any iOS app distribution option — including the App Store, an alternative app marketplace, TestFlight, an App Clip, volume purchases through Apple Business Manager and Apple School Manager, and/or a custom app."
> First annual install. The first time an app is installed by an account in the EU in a 12-month period. After each first annual install, the app may be installed any number of times by the same account for the next 12 months with no additional charge.
This is on a per account basis - not a per device basis. The install for a phone and iPad are the same install.
Note there is zero way to audit this charge from apple. There's no way to identify an install on iOS anymore unless the user signs in/signs up for an account.
There's also usually up to a 10% "breakage" between people who install from the App Store but never run your app.
You don’t have to sign up for an account, an app can install some type of opaque object in iCloud that they can use to identify someone who uses their account.
If I delete Overcast from my iPhone or install it on a brand new iPad, all of my data is kept in sync. That data is stored in a database where the user id is that opaque blob.
Marco Arment (the author) does all he can to discourage users from storing a user name/password/email address as part of the login and only requires you to have one to associate your user to your account to access your podcasts on the web.
Also, updates do count.
"A first annual install may result from an app’s first-time install, a reinstall, or an update from any iOS app distribution option — including the App Store, an alternative app marketplace, TestFlight, an App Clip, volume purchases through Apple Business Manager and Apple School Manager, and/or a custom app."