It's really confusing to start with isn't it?
No, an Itti is an 'all in two' - it has built in waterproof layer that doesn't need a wrap. And the insert is a snap in one that lays inside rather than in a pocket.
Confusingly, some people call them 'all in ones', but I tend to refer to these as the ones that are one complete piece with sewn in insert.
Also, some people use fitted and sized as the same thing.... An Itti IS sized (rather than birth to potty/one size).
Confused? I am
So, you can have fitted either one size or sized. And you can have pockets/AIO/AI2 that are either one size or sized s/m/l...