Technically, sorry Deus, they are not a T1 if they stop producing insulin because THAT depends on what kills the Beta cells.
If it's auto-immune antibodies (ie GAD65 antibodies) then they are T1.
If they haven't got em or had em, (or enough of em, not sure if they are intrisically bad or whether they just gang up and riot, or what) then that means it ain't T1.
It's my understanding that T1s have sheadloads of the ruddy things on diagnosis but once they have done their dirty work, they disappear either entirely or almost entirely, not sure which - but anyhow it has been said you have to do that test within the first 6 months of diagnosis to get a meaninful result. I mean I fully expect that I haven't got any by now, but that doesn't mean I've Shape Changed into T2 or anything else other than T1, does it?
And talking of shape, how do you therefore explain my friend Lanky L(surname) - as she was known at school, she always has been thin and still is now she's 50-odd. She's been T2 for about 10 years now! Tall and slender. We have had quite a succession of thin T2s on the other DSF plus more than several Mature T1s.
Plus I've been similar to a barrel on legs at one time in my life, whilst I've had T1. Certainly not before I was diagnosed though. And it was caused by totally normal classical means - ie eating far too much too fattening food. So I stopped doing it and got rid of the barrel.
And not every T2 has missing Phase 1 insulin, and not every T2 has insulin resistance, and not every T2 will ever kill all their Beta cells, or need insulin, not every one will have hyperinsulinema to cause weight gain - the list goes on ad nauseam.
In comparison to T2, the mechanism (? is that the word) of T1 is pretty straightforward to understand, notionally that is*. T2 ain't ..... I think it's a list of differing symptoms and causes that are all lumped together for convenience and it'sa wonder anyone gets treated correctly for it since the tests aren't done to establish which bit's gone wrong in the first place.
* and as every T1 will agree it isn't straightforward at all .....