You got me interested, so I searched around and found this:

So, if I understand this correctly, the only fundamental difference between level 4 and 5 is that 4 works on specific known road types with reliable quality (highways, city roads), while level 5 works literally everywhere, including rural dirt paths?

I’m trying to imagine what other type of geographic difference there might be between 4 and 5 and I’m drawing a blank.