questions about billy

two questions here,(please exscuse my bad english if you see any mistakes)
1)Why in loop 100 billy didn´t copy unforgettable?, we got explanations of why billy couldn´t copy fuuko and tatiana, it also makes sense that he couldn´t copy isshin, but i don´t remember this being adressed at all, (tho i might be wrong)
2)right now in loop 101 nico has unforgettable, so will billy copy this one? i mean it could def help him a lot and he could learn how to use every ability he copied + soul stuff very easily.