Adding a person needs four things: their name, how to reach them, their role, and their territory.
You do not have to wait for anyone to accept an invitation. A person added here starts receiving alerts immediately — the account is only needed to sign in and look around.
When they do sign in for the first time, their email is matched to the entry you created and their role and territory attach automatically. There is no second setup step, and nothing to re-enter.
This is why loading five hundred people from a spreadsheet before anyone has an account works properly: the alerts are already routed correctly, and each person's access resolves itself when they arrive.
The match is on email address. If someone signs in with a different address from the one you entered, they'll arrive with no role — correct the address on their entry rather than creating a second one, or you'll end up with two records and only one of them receiving alerts.
Read next: Bulk import from a spreadsheet →