Hello Se-UK Moon,
DSO, in essence, is related to sales outstanding for different customers expressed in number of days.It helps the business to keep track of receivables from customers. In DSO calculation, it is the customer master number which is the focus and not the GL account. As regards the 'GL account' which you are referring to in the dynamic selection of RFDRRSEL, if you hit F1 key, you will get below information -
"This field contains the number of the G/L account to which the transaction figures are updated".
In my view, this restriction(selection parameter) is not the right way to get the desired output.
Further, you have mentioned that RFDRRE05 did not work as expected. What exactly was the desired output? Could you give some more information, say with an example/screenshot to explain the issue in a better way?
Hope above information was helpful.
Regards,
Avinash