You're confused because there are different concepts of what constitutes an AIO.
The T&T AIO described by Steph is really just a shell, if I'm understanding her right. Some people call an AIO a shell that has an external soaker pad. This means that you lay the soaker pad into the shell. I don't personally consider this an AIO, although I may go against the grain in the diapering community by saying so. I consider this a cover with a diaper. Some people make it a snap-in soaker, and that's closer to an AIO, especially if you never unsnap it for washing and it's always ready to go.
I consider an AIO to be having the outer waterproof layer and the inner absorbant layer in one package all sewn together. You can also (which I do) add snaps for a snap in soaker to boost absorbancy and decrease drying time.
So, that being said, I think the only way that you can do an AIO with sewn in absorbancy and hidden PUL and T&T is if the absorbant layer (I'm going to say 'hemp' now, it's shorter to write) is only a soaker pad, rather than being the entire shape of the diaper. Did that make sense? I usually make my hemp the same shape as the outer. But you can't do a hidden layer and T&T like that as the hemp will touch the outer flannel. But if you make the hemp only the size of a soaker pad and stitch it onto an inner fleece layer, it won't touch the outer flannel after T&T.
The AIO described above by Steph doesn't have a hemp layer sewn in. Therefore no hemp touching the outer flannel. Of course, it's possible I misunderstood her and she's really describing what I just did.
Hope I helped and didn't confuse you further.