Beginning on October 1, 2008, and thereafter, agencies shall ensure that decisions to use interagency acquisitions are supported by best interest determinations, as described in the attached guidance. Agencies shall further ensure that new interagency agreements for assisted acquisitions entered on or after November 3, 2008, contain the elements enumerated in Appendix 2 or follow the model agreement in Appendix 3. Agencies shall use the checklist at Appendix 1 to facilitate the clear identification of roles and responsibilities. Agencies shall also consider modifying existing long-term interagency agreements for assisted acquisitions in accordance with this guidance, as appropriate and practicable.