(3) Subject to paragraph (4), for the purpose of calculating an earnings factor for assessing entitlement to any benefit under the legislation of Great Britain, Northern Ireland or the Isle of Man in accordance with Articles 14 and 16 to 24, a person shall be treated for each week beginning in a relevant income tax year commencing after 5 April 1975, the whole or any part of which week is a contribution period completed as an employed person under the legislation of Ireland, as having paid a contribution as an employed earner, or having earnings on which primary Class 1 contributions have been paid, on earnings equivalent to two-thirds of that year’s upper earnings limit.