Actually, the DL RES agent only has access to the internal DL RES system. That system only has status of DL flights, either DL metal, conx, or code share. The DL system does not have access to inventory status of partner carrier flights that are not codeshare. Thus, when you ask them to look at NW flights (for example), they really can't. As mentioned above, a travel agent or any web site using a Global Distribution System (GDS) like Sabre or Worldspan has access to all airlines inventory status.