Using Rocksmith 2014 on PC from Steam.  I found the Clash song "Stay or go" in Ignition but it said it was "official" and I couldn't down load like the other 2014 DLCs.  I found it on Steam, purchased but it didn't show up in song list, probably because I don't have original rocksmith.  Do I have to buy original Rocksmith game now also?  BTW, the disk import tool says you need Rocksmith and I'm thinking that only imports original songs (most of them) that come with the original game.  Help appreciated.  Looked around a lot and still confused. :(

DLC from RS1 will work even if you don't own RS1, you might just need to restart the game for it to properly populate the song list.

 

As for the disk import tool, it allow you to access the songs that were included in the first game (not the DLC) but for this, you do need to own the original game on steam.