CIL - Social housing relief exemption on Council land - Public forum - Planning Advisory Service (PAS)

It seems clear that SHR exemption must be sought by the land owner and prior to commencement. The Council wants to sell the land to an affordable housing provider so does Reg 51 apply in so far as land disposal and transfer of exemption? OR, should the process be the affordable provider applying again for exemption and prior to commencement? Either way I suspect a conditional approval for the exemption can be accepted provided the affordable homes come to fruition? I think the affordable homes provider should provide details about the nature of tenure prior to occupation. Is this a route that oters have followed/experienced?