Yes, but with existing music, current lawsuits use the fact that the music under dispute was playing on radios, nightclubs, tv, etc. So there is the possibility

Yes, but with existing music, current lawsuits use the fact that the music under dispute was playing on radios, nightclubs, tv, etc. So there is the possibility of the other artist having heard of it. If the music is stuck inside of a gigantic database that nobody has accessed, it becomes much easier to prove that you in fact never heard it.