Hi,
You may need to do selective load from dso1 to dso2.
you need to find the req1 to re3 and find proper selections to load data. once you got the proper selections then you can load them to DSO2.
When delta loads are failed, always need to be taken on the day itself once you lost records. manual efforts to be needed. Better to create messages to your delta process chains about failures or success.
How much data you have at DSO1 as of today?
Thanks