In PCI-Express and alike network systems, back-up copies of recently sent packets are kept in a replay buffer for resending if the original packet is not well received by an intended destination device. A method for locating the back-up copy in the retry buffer comprises applying a less significant portion of the sequence number of a to-be-retrieved back-up copy to an index table to obtain a start address or other locater indicating where in the retry buffer the to-be-retrieved back-up copy resides. A method for skipping replay of late nullified packets includes deleting from the index table, references to late nullified packets.