AB- is the only type rarer than AB+. The positive and negative refer to RH factor. I’m AB+ (positive). Negative in any blood type is rarer than positive, but since AB anything is only 4% in the US, both versions are the rarest ones.
I tested my own blood years, ago in school science class. Years later it was confirmed correct, when I donated blood. Which even later they would not let me do, since I had spent time in Europe in the ‘80s. Mad cow, you know. Never mind that I didn’t eat beef while there...
They used to have it set up that you could donate blood and tell them “do not use” because of a medical problem or whatever, and they would go ahead and tap the blood in order to protect the person’s privacy. Like if it was a church blood drive and xhey didn’t want to say “no I don’t want to give, I have GRIDs” because of the disfavorable social consequences of coming out with having a disease like that.