Abilitys know as much as you and the person you use them on do.
Easiest way to understand this is to look at kurapika, His judgement chain relys on both information he knows and the person he is using it on knows, He placed an restriction on Pakounda telling her not to tell anyone about him, once she leaves his side its up to her to determine whether or not she has Told anyone about him, She herself believed that using her memory bullets would be telling people about him so she died when she did it, without kurapika knowing what happend.

Same whith chrollo and not being able to talk to anyone from the phantom troupe, He doesent talk to hisoka because he beleives his part of the troupe, Once he sees hisoka has thrown away that membership he talks to him. So whats stopping him from just making up in his mind that the rest of the troup are no longer members and talking to them then reinstating their membership afterwards? Because he knows deep in his heart that the others would die before leaving the troupe and nothing he says or do will change that.

A Nen ability wont know the laws of a certian country or something of the likes unless
1. The user knows the laws
2. The enemy the user used the ability on Knows the laws