4.I chose the registration date first, as this is the easiest confirmation. We are looking for 1 letter from the cryptopia in the mail using the built-in search. There will be a registration date, BUT this is your local date, and you need a date in New Zealand time. To do this, open Google and search (what time it is in New Zealand) then by the time that was in your letter, you either add or minus the difference between your local and New Zealand.It may turn out to be 1 day more, maybe 1 less, or maybe get the same day.
Can be easy
only if you saved the automated replying mail back then. If not, you can forget about it.
5.Secondly, I chose the output date that I had last.
Same for this option, easy only if you can recall after 3+ years and if you had only 2 or 3 assets/ coins/ tokens there. If you had more or make a bunch of transactions each week, then you can forget about this option too. In other words, the method/ way that they choose to verify users are based on memory which is near to absurd for such a matter. More than a lot of users that had their funds there will be stuck and not able to verify themselves with this "system" and that means that those funds will be claimed from Grant Thornton.
Does anyone know the last date of filling up the form ?
No, at least until now. Nothing mentioned for any deadline.