An apparatus of a next generation Node B (gNB) Distributed Unit (DU) comprises one or more baseband processors to transmit one or more retransmitted Packet Data Convergence Protocol (PDCP) Protocol Data Units (PDUs) received from a gNB Central Unit (CU) to a user equipment (UE), and to feed back not only a latest, in-sequence New Radio User-plane (NR-U) Sequence Number (SN) to the CU for Release 15, but also a highest, in-sequence successfully delivered/transmitted PDCP SN, optionally, with a NR-U SN up to which the reported PDCP SN should be applied, which can provide an exact range of successfully delivered/transmitted status for retransmitted packets even in case of DU's re-ordering based on PDCP SN before transmitting to the UE. The apparatus can include a memory to store the reported PDCP SN and NR-U SN.