I am pretty sure that the aircraft arrives still officially registered under the FAA so you have all the local CAA paper to be issued, radio licences, AOC etc. Also there may be quite a lot of maintenance actions to be carried out to get it fully kitted out to air nz specs. Also it is quite normal to not incorporate it fully into the flying programme for a few weeks and just to use on an adhoc basis to iron out any kinks before it's full time intro.
Check out this video to see some of the things that can occur:
https://m.youtube.com/watch?v=LDdY21Y2DGI