The time limits specified for the Corporation's initial response in Sec. 2507.5, and for its determination on an appeal in Sec. 2507.7, may be extended by the Corporation upon written notice to the requester which sets forth the reasons for such extension and the date upon which the Corporation will respond to the request. Such extension may be applied at either the initial response stage or the appeal stage, or both, provided the aggregate of such extensions shall not exceed ten working days. Circumstances justifying an extension under this section may include the following:
(a) Time necessary to search for and collect requested records from field offices of the Corporation;
(b) Time necessary to locate, collect and review voluminous records; or
(c) Time necessary for consultation with another agency having an interest in the request; or among two or more offices of the Corporation which have an interest in the request; or with a submitter of business information having an interest in the request.