Corpora (Oct 19, 2019) says Principalities need to have at least 100 members.
Between 2012 and 2017, NZ had had a stable subscribing adult membership of around 160-170; by early 2020 this had grown to a high of 214, by late 2023 it was nearly 250.*
(* Membership numbers were expected to drop as a result of COVID effects but this did not happen, quite the opposite.)
This long period was considered to see whether NZ’s popular 3-year membership option has affected or inflated paid memberships (as has been suggested); this does not appear to be the case.