RRB - Revenue Surplus (RA method 15)

Hi Experts,

The help documentation for RA Method 15 (revenue from RRB) says that it cannot calculate reserves.

Can anyone please explain this in details?

Does it mean that in a scenario where there are no actual cost/hrs to be invoiced, but if during RRB if we enter some advance amount when creating billing request, how will the RA in that scenario work? Will there be a deferred revenue posted in BS?

Thanks,

Krishna