It is a CNZ requirement that all Coastguard Skippers hold what Maritime NZ refer to as an ISC, an industry Specific Certificate.
Essentially Coastguard runs a training framework designed to meet the needs of Coastguard work that is approved and regularly audited by Maritime NZ. Volunteers who progress through the matrix and have the approval of their unit can ultimately obtain an ISC to master a Coastguard Rescue Vessel.
Someone joining Coastguard with an existing qualification such as an ILM or SRL can have some components of the training "RPLd" or covered by Recognition of Prior Learning but there will be some components that they will have to cover off before a CNZ ISC will be issued.
An ISC is specific to a Coastguard Vessel(s) and area(s) and isn't transferable to other commercial vessels.
Howzat! :-)