(1) Subject to subsection (2), the provisions of the Principal Act referred to in Schedule 3 shall apply subject to the amendments specified in that Schedule.
(a) Subject to paragraph (b), this section shall apply as on and from the times at which the Convention set out in the Schedule to the Double Taxation Relief (Taxes on Income and Capital Gains) (United States of America) Order, 1997 (S.I. No. 477 of 1997), has effect in accordance with paragraph 2 of Article 29 of that Convention.
(b) Where, in relation to a person, paragraph 3 of Article 29 of the said Convention applies in respect of the period specified in that paragraph, the Principal Act shall apply in relation to the person in respect of that period as if subsection (1) had not been enacted.