Failed transactions passed to hook?

Quick question.

I am writing a function that runs on gform_paypal_post_ipn and does different things based on the txn_type returned from PayPal. I need to do nothing at all with failed transactions.

I am thinking that something like this to just stop my function on failed transactions would be no harm, but is it superfluous - are failed transactions already filtered out before the gform_paypal_post_ipn hook runs?

if( $ipn_post['txn_type']=='subscr_ failed')
	 	 return;

Thanks.