For purposes of paragraph (1) of this subsection, the term “wages” includes such remuneration for services covered by an agreement made pursuant to section
3121
(l) as would be wages if such services constituted employment; the term “employer” includes any American employer which has entered into an agreement pursuant to section
3121
(l); the term “tax” or “tax imposed by section
3101
(a),” includes, in the case of services covered by an agreement entered into pursuant to section
3121
(l), an amount equivalent to the tax which would be imposed by section
3101
(a), if such services constituted employment as defined in section
3121; and the provisions of paragraph (1) of this subsection shall apply whether or not any amount deducted from the employee’s remuneration as a result of the agreement entered into pursuant to section
3121
(l) has been paid to the Secretary.