I am unsure as to how the process works with the Police in NZ, but perhaps contacting the UK equivalent will give you some idea?
http://www.acpo.police.uk/certificates.asp
For any enquiries relating to Police Certificates please contact ACRO Customer Services on
Tel: 0845 60 13 999
via email: customer.services@acro.pnn.police.uk
or write to ACRO at the following address enclosing a stamped addressed envelope.
ACRO
PO Box 481,
Fareham,
PO14 9FS
My personal opinion: The clearance should be as recent as possible. The logic behind this is that the purpose of the certificate is ascertain a subjects good conduct. As such, the more recent the clearance certificate is, the less likely you have been involved in any matters.
Australia typically accepts certificates up to 12 months old but there does not seem to be any specific guidance in regards to any other common law jurisdiction. It would be difficult to estimate what the permissible period is for the UK, but as the validity on CRB's is simply stated as 'as recent as possible', it would be prudent to assume a similar policy is in place.
Obviously the harder the document is to procure, the more leeway you will be afforded in regards to time.
Sorry for being quite vague, but I hope this information is of some help!
