I think you need to check with INZ about the timings you have in mind. If someone has had the longest visa they could be issued at the time (not talking about any extensions), then INZ require them to be out of the country for the equivalent amount of time before they can come back again. This can partly depend on whether or not they stayed for the whole length of the visa they had, as well as how long it is since the last trip when they want to travel again. So I don't think you can be sure of working this out right for yourself - ask INZ, to be safe.