In appendix 5 it says...
The qualifications in this list do not require assessment by the New Zealand Qualifications Authority (NZQA). Qualifications will qualify for points on the basis of their assessed position on the Register (see SM14.15 of the Skilled Migrant Category).
...then if you click on the
SM14.5 link it brings up a little table showing how many points you get for the various types of qualification. It doesn't, however, separate the different types of diploma.
I can only assume that, if your diploma type isn't shown on the register, you may have to have it assessed by the
NZQA but have a dig around the other links to see if you can find anything more definite first.