You should get green slip quotes when you want to renew registration or start a new registration in NSW. You cannot register a vehicle or get green slip prices more than 3 months in advance.
For a renewal, you need the registration commencement date on your rego papers. You can renew registration up to 3 months before your registration is due or up to 3 months after it was due.
You must start a new registration if your registration is more than 3 months overdue, because Service NSW will cancel your registration. Your vehicle will need a blue slip and the registration commencement date will be today.