You’re so close.
You just listed four options, but still argue that’s a ‘binary’. Every time you look closer, you’re going to find another outlier to categorize. Eventually, it starts to make more sense to look at it as a spectrum instead of a rigid set of ‘either A or B or AB or {NULL} or …’
Lmao. You realize the rainbow is a SPECTRUM, right? If I show you a rainbow, can you draw the line where green stops and teal begins?