All the information on the first CD will be the same on the latest CD, it is just an upgrade with additional information.
Hi KHP...
Not what I heard (even though I'm not a NZSG member so have never owned or used either CD so what do I know

NZSG Vol 5 contains a lot of info that was not allowed to be copied over to the Kiwi Index.
Likewise the Kiwi Index contains a lot of new info that had been transcribed since Vol 5 was released.
The two CD's are complementary rather than Kiwi superseding Vol 5... although, as I said, that's just what I've heard.
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We are pretty sure he went to Ellerslie Primary School, Auckland [...] we did find his foster brother there.
Hello Denise...
So are you saying you've found and viewed Ellerslie School records for your grandfather's foster brother.
If so, do you have a record of these records. I'm curious as to what they are (e.g Form No.20 - Class List, Form No.19 - Examination Schedule etc).
To be honest, I'd say the pretty comprehensive Ellerslie School records held by Auckland Archives are the only ones surviving from 1897 to 1907. If you've searched them and your grandfather isn't mentioned then I'd say he didn't attend that school.
Regards
Beg