Personally, I think you need to check more than "just" table EKKO...
(http://help.sap.com/saphelp_sm32/helpdata/en/8d/bc383fe58d5900e10000000a114084/content.htm)
That link also explains how you could reconcile between BW and ERP... might be usefull to do so for your "date".
You should be able to retrieve which documents were sent over via the (info) IDocs (if they're still available in ERP). As per your comment "The Info Package which indicates that an x amount of records were transferred but not received" that means the ERP system knows which records were sent out.