How does NEC4 Option Y(UK)2 work?

Option Y(UK)2 is the secondary option that makes an NEC4 ECC comply with the Housing Grants, Construction and Regeneration Act 1996 as amended, and it works by mapping the Act's notices onto the clause 50 and 51 machinery. Under clause Y2.2 the date on which a payment becomes due is seven days after the assessment date, and the final date for payment is fourteen days after the date on which payment becomes due, or a different period if the Contract Data states one. The Project Manager's certificate under clause 51.1 is the notice of payment required by section 110A of the Construction Act, stating the amount due and the basis on which it was calculated, and because clause 51.1 requires it within one week of the assessment date it should be in the Contractor's hands by the due date. Where no certificate is given, the Contractor's application for payment stands as the notice under section 110B. Under clause Y2.3 a Party which intends to pay less than the notified sum gives a notice of intention to pay less not later than seven days before the final date for payment, stating the amount it considers due and the basis of that calculation; without it, section 111 requires the notified sum to be paid. Under clause Y2.4 a suspension by the Contractor under section 112 of the Act is a compensation event, so the cost of a lawful suspension is recovered through clauses 61 to 66 rather than as damages. What goes wrong: the certificate is issued without a basis, so it is a weak payment notice; the Pay Less Notice is given by the Project Manager rather than by the paying Party; the final date is counted from the certificate rather than the due date; Contract Data or Z clause periods replace the fourteen days and are not diaried; and a Contractor suspends without the notice the Act requires.