If there is an overpayment, and if the clmt would otherwise have been entitled, I don’t see why diminishing capital can’t be entered onto IBS. At worst, all it needs is a new capital code to identify the capital in question as diminshing.
Also, IBS has a “tick-box” specifically for underlying entitlement inputs. So, again, I don’t understand what the problem can be.
NB: Just a note of caution. If there has been a period of nil entitlement, a new claim will be needed for any on-going benefit to be awarded. So, you need to make sure that any period of underlying entitlement is given an end date on IBS….. (Erm, yep, I have overlooked this on more than one occasion….. *sigh*).
Regards