two people who I know that logged their application later than me has been approved residence in April
It's not a race with three horses! INZ are dealing with hundreds of thousands of cases, and your cases are just specks in that great sea of paperwork. They won't always finish up in the same office to be dealt with throughout, even if they were originally submitted in the same place. See this old post to imagine it.
https://www.enz.org/forum/showthread...332#post558332
Reasons why a case can get finished sooner. 1) All the people asked to verify pieces of evidence replied by return, when on another case, they weren't in any hurry. 2) One case has claimed the minimum of points, so has fewer things to be verified, whereas another may have several qualifications, several lots of work experience and partnership proof.