Hi,
Assuming as your bw cube have 3-4 yrs data.
You enhanced data source and need historic data for enhanced field.
If yes then you can delete and reload whole data. You delete old init and reinit.
Set the delta pointer.
at your data flow if you have dso and all key figures over write property then you can just reload last 4days(missed) delta records thru repair full request with proper selections.
About init you can delete and reinit.
Please check above suggestions ad revert back if have any doubts.
Thanks