that in the case of an individual who has at least 6 quarters of coverage as defined in
section 413 of this title and periods of coverage under the social security system of a foreign country which is a party to such agreement, periods of coverage of such individual under such social security system of such foreign country may be combined with periods of coverage under this subchapter and otherwise considered for the purposes of establishing entitlement to and the amount of old-age, survivors, and disability insurance benefits under this subchapter;