vlr+hlr: Insert Data

What should we do if the HLR sends no Insert Data? When a subscriber does a Location Updating, the VLR sends a Location Updating request to the HLR. The HLR typically responds with a Location Updating Result as success and, in a *separate* message, sends an Insert Data to the VLR to tell it the subscriber's MSISDN. So it is possible to do a successful Location Updating without being told the MSISDN (as my test verifies). What should the VLR do if it never receives the Insert Data from the HLR? In that case the subscriber is attached but cannot be reached by MSISDN. Should we actively wait for Inser Data and reject the subscriber if not successful? It would be fairly easy to just send the MSISDN along in the Location Updating Result. Why this separate message? Thx, ~N