See Fair Work Act 2009 s.186(5)
One of the requirements for the Fair Work Commission to approve an enterprise agreement is the requirement that the enterprise agreement:
There are 2 ways the nominal expiry date can be expressed in an enterprise agreement:
An enterprise agreement does not have to state a specific date to meet the requirements of s.186(5). An enterprise agreement can specify its nominal expiry date by reference to the end of a period of time after the agreement’s commencement or approval.
However, one of the issues with specifying a nominal expiry date by reference to the date of approval is that the parties do not know when the Commission may approve the agreement, so they do not control precisely when it will nominally expire.
Agreements continue to operate after their nominal expiry dates until they are replaced or terminated by the Commission.
This means that the provisions contained within an old enterprise agreement will continue to apply to the parties covered by the agreement after the nominal expiry date. These provisions are fully enforceable and must be applied, even if the nominal expiry date was several years before.
When an approved agreement continues to operate, the provisions of the National Employment Standards (NES) will apply in circumstances where an entitlement in the agreement is less than that provided for by the NES.
 Newlands Coal Pty Ltd v Construction, Forestry, Mining and Energy Union  FWAFB 7325 (Hamberger SDP, McCarthy DP, Blair C, 15 December 2011) at paras 28–29.