Some certificates will expire after a certain period. The Council certificate is generally valid for 90 days, and an Owners Corporation certificate can quickly become outdated if payments are made quarterly. A title search is generally only acceptable for 120 days.
A prospective purchaser would be entitled to require new certificates, as the obligation is on the vendor to disclose accurate and complete information about the property. If the vendor doesn't, they risk the purchaser walking away from the contract at any time prior to settlement - as is the purchaser's right according to the Sale of Land Act.