We have table ROOSPRMSC which stores the successful last delta request time stamp for each data source(if it is delta enabled).
When ever the delta IP got successful, the time stamp will get update in the table (it doesn't bother about whether request is there in target or not). If the over all status of IP comes to green, then time stamp will get updated to system table.
So when ever you have any failed delta request or if you want to load the previous delta request again, follow the below steps.
1) Open the failed request or request you want to run again by going into manage tab of target and click on monitor of request, then change the over all status to red.(you can do the same like, open the delta IP in RSA1 --> on top click on monitor --> in left side you will get all requests)
here system will prompt you message saying that" you have to perform repeat delta".click on "Repeat Delta"
2) Now goto target and make the request red and delete it.
Now run your delta IP, it will pick earlier and present delta records.
Note: If you are already deleted the request from target, then open the request in RSRQ and make the request to Red. This is enough to get the last delta records.
Hope it helps...