The term “employment” shall not include services performed for an employing unit which is subject to this Act solely because of subsection A of Section 245, if and while such employing unit, with written approval of the Director, duly covers under the unemployment compensation law of another State all services for it which would otherwise be covered under this Act, provided that those individuals whose services are hereby excluded shall be counted in determining whether such employing unit is an employer under Section 205. Such approval may be withdrawn by the Director upon written notice to such employing unit, addressed to its last known address and, in the event of such withdrawal, such services shall again be deemed employment subject to this Act as of the date such services ceased or could have ceased to be employment, by the reasonably prompt filing of an application for termination of coverage, under the unemployment compensation law of such other state.