What transactions are restored when I call restoreCompletedTransactions if the user has bought two or more non-renewing subscriptions one after another say one month apart. Do I get transactions for both of them with transactionState SKPaymentTransactionStateRestored or only for the one that is currently valid (meaning within current subscription period) ?
You get all the transactions, that have been made. In the non-renewing case, this means a lot)
When your application restores previous purchases, Store Kit deliveres EACH transaction to your application.
EDIT Apple doesn't restore non-renewing at all, so you habe to create that mechanism yourself, otherwise, you'll be rejected—that really happened with my app.