623. Where a taxable supply is made under a contract to construct, renovate, alter or repair an immovable or a ship or other marine vessel, the following rules apply:(1) any consideration for the supply that became due or was paid without becoming due after 31 August 1990 and before 1 July 1992 as a progress payment required under the contract is deemed, for the purposes of Title I and of this Title, to have become due on 1 July 1992 and not to have been paid before 1 July 1992;
(2) no tax is payable in respect of any part of the consideration for the supply that may reasonably be attributed to property delivered and services performed under the contract before 1 July 1992; and
(3) where paragraph 3 of section 86 applies in respect of the supply, tax is payable in respect thereof and the construction, renovation, alteration or repair is substantially completed before 1 June 1992, the construction, renovation, alteration or repair is deemed, for the purposes of Title I and of this Title, to have been substantially completed on 1 June 1992 and not before that day.