Paypal IPN variables - what kind of failed transactions are retried

I'm developing a module that handles IPN calls from Paypal. From the documentation, I see that when txn_type = 'recurring_payment_skipped', the IPN will be retried up to 3 times, 5 days apart. But what about other transaction types, such as 'subscr_failed' and 'recurring_payment_failed'? Do they enter the retry process as well or are they sent once only?

Thanks!

PS: I just moved this question from money.stackexchange.com and I'm only putting it here because I don't see any other SE website that's more fit.