Help Some particular songs won't appear in my library?

[Yolandi and ninja]

I use YouTube to mp3 converter for a lot of my songs. Then I open them on Google play. This works for all songs except for every song by 'Girls Generation' for some reason. I try to download them again but they still never show up in the library. I even found other videos of the same song to see if that would fix it but still it doesn't work.