I got the answer.
Mere coincidence , just went down the hierarchy of Billing Cycle and got the answer in Rate Types definition.
Please refer the screenshot
If that highlighted Checkbox is ticked for a Rate Type and the "R" checkbox is kept unchecked then that Rate Type + Rate Category combination will be determined even though a Device with that Rate Type haven't been maintained in the Installation.
Doing F1 with these 2 Checkboxes will clarify everything 