Deepslate and tuff badges not generating properly below y=0

Deepslate and Tuff badges seem not to generate properly below y=0
I've explored for quite some time the new caves, and most tuff and deepslate bedges generate between y=16 and y= 0. Some badges generate low enough for deepslate and tuff to be below y=0 (I've found deepslate up to layer y=-8) but not lower.