The difference is the duration; and I would guess its done due to the vagaries of measurement as much as anything because its common for the initial numbers to end up being revised later. So 2 consecutive quarters of negative GDP growth is a technical recession, and beyond that you're in a real recession.

But the cynic in me will always suggest that while economists sometimes seem to think what they're doing is a hard science, a lot of it seems to be more about the feels and what is expedient to their political view point.

Then on top of that, over the years i've read various arguments that GDP is kinda a piss poor measure of the economy anyway, and there's more holistic ways of measuring how things are going. This article sums up a bunch of the opinions about it, of whose Craig Renney's is the one I probably put more stock in - along with those suggesting using the Sahm Rule given it looks at employment which is probably a better measure for how actual people are getting along.

https://www.interest.co.nz/economy/124432/we-asked-twenty-economists-how-they-would-define-recession-new-zealand