When you can remember seeing RNZAF de Havilland Vampire flying.
... and the RNZAF Sunderland flying boat based at Hobsonville taxiing under the Harbour Bridge, NAC DC3s and the de Havilland Herons that flew provincial routes.
Not to mention the TEAL Lockheed Electras that flew the Tasman out of Paraparaumu, pre-Rongotai.
And that Whenuapai was Auckland airport pre-Mangere.
I remember and actually saw all this.
You know you're old when your memory plays tricks on you :)
I think you'll find that the Electras arrived after Rongotai and it was probably DC6s that you saw.