Ann: Change in substantial holding, page-43

Folks
In the half yearly accounts, they indicated that they changed the forecast amortisation rate to 46% (from 43%) on the PDLs.

Can someone help me understand what that actually means (is it that they have applied a 46% discount to the face value of the PDL), and if that is the case surely that is not very precise (you have different credit profiles, different types of debt, different ages for the debt), so I'm sceptical that they can do that and reflect that as an asset on balance sheet....anyone know?