I mean, in the Alfredo scenario maybe I’d call it chicken spaghetti Alfredo? Like, that seems totally reasonable to me I just don’t have a go-to term for it because I don’t usually eat that. I can say that I live in the U.S., and would be very confused if an acquaintance or a restaurant indicated we were having fettuccine Alfredo and I ended up eating spaghetti. In the first case I wouldn’t mind at all, but would probably be quietly amused. In the second, if it was a nice restaurant I wouldn’t mind probably say something, if it wasn’t I would just eat my food but probably never go back unless it was exceptionally good.

If I’m having red meat sauce that typically goes on spaghetti at home I’ll probably call it bolognese, because that’s what I usually make. Outside of my home it’s still very often a bolognese, but often the more broad ragu. The biggest confusion I would have if presented with the concept of ‘spaghetti sauce’ is whether or not there is going to be meat in it, as a simple marinara is frequently referred to as spaghetti sauce as well.