Deciphering IRD's new acronyms - IIT return and ITN return

This tax season I got an email from IRD reminding me I had to file my return. This happens every year and is usually not a surprise. However this year, the returns were slightly different. They said:

The 31 March 2019 IIT return for {person} is due 8 July 2019.

and

The 31 March 2019 ITN return for {company} is due 8 July 2019.

I’d never heard of an IIT return or an ITN return. I searched around and couldn’t get any results on Google or IRD’s website search. However, my best guess at the acronyms is:

IIT Return: IR3 - Individual Income Tax Return
ITN Return: IR4 - can’t think of a good explanation for this acronym

I think IRD has renamed these in their recent system upgrades and I suspect they’ve renamed all of their returns. If you come across any other acronyms, let me know and I’ll add them here to help others out.