I am similar to you, just watching things here as an outsider… It seems 400g is the weight of the fat and the meat, not just the pure fat and protein, that’s why people wrote they eat way less then 9 oz fat…
I don’t know how people know the macros of their food, I haven’t the vaguest idea about my ham (except it’s extremely fatty, way fattier than the pork chuck I usually buy and that’s obviously not lean either), I try to track but it’s lots of guesswork. It’s no problem now as it’s smoked ham and I eat a tiny amount of it but when I eat mutton and a way bigger amount, I am in the same situation, I simply have no idea how fatty it is… I am a newbie at it but I can’t imagine I ever will be able to guess the fat content of my meat. Maybe the people who do PKD buy it with some correct label…? My meat has no label at all.
To me, it’s amazing people can eat that fatty on carnivore and I wonder if they need some training to do that as I definitely will need it even though my goal isn’t that high fat:protein macro now (I easily ate way more fat while I ate a significant amount of plants on keto, I even could eat certain tasty fats alone if I wanted but it suddenly changed on carnivore, I am a newbie at this). I imagine if someone has a very good reason, it motivates them but still, the body might have some difficulties first… I feel very lucky that I am healthy and my current 1:1 ratio works almost perfectly for me now but I have to learn to eat a bit fattier soon.