Not quite true… Hamilton’s station was originally 2XN, but it was part of the NZBC, it was never a private station then… X’s denoted a mix of purely commercial (Z) and non-commercial (Y) stations at that time.
Nelson’s 2XN was 2YN from 1937-1947, that one was a private station, 2ZR, which ran from 1932-1936. Basically all radio stations in NZ from 1937 were Govt owned except for 2ZM Gisborne (until 1944 when owner Percy Stevens died) and 4ZD (Dunedin) until Mediaworks bought that one. Callsigns with an X in them didn’t denote private stations again until Radio Hauraki spang up.
I’ve been building a wee timeline on-and-off for a past 15 years or so, but I’ve only got to the 1970’s (when the confusion begins, I guess). I posted a consolidated NZ Radio dial image from the 1920’s a while back, in the NZ Radio History thread. I should post some more at some stage, when I get some time.