(15)Regular rotation of credit rating agencies issuing credit ratings on re-securitisations should bring more diversity to the assessment of creditworthiness. Multiple and different views, perspectives and methodologies applied by credit rating agencies should produce more diverse credit ratings and ultimately improve the assessment of the creditworthiness of re-securitisations. For such diversity to play a role and to avoid complacency of both originators and credit rating agencies, the maximum period during which the credit rating agency is allowed to rate re-securitisations from the same originator must be restricted to a level that guarantees regular fresh assessments of creditworthiness. Those factors, together with the need to provide certain continuity of approach to credit ratings, mean that a period of four years is appropriate. Where at least four credit rating agencies are appointed, the objectives for a rotation mechanism have already been achieved so the requirement to rotate should not apply. In order to ensure real competition, such an exemption should only be applicable where at least four of the appointed credit rating agencies rate a certain proportion of the outstanding financial instruments of the originator.