By playing through the career mode, you have unlocked all of the single player songs. The 34 or 36 out of 42 only means that is how many songs you completed in that career. If it says 34, go back and count through how many you didn’t complete and it will add up to 42.

Now, there are songs to unlock that can only be unlocked by completing a multiplayer career mode. Personally, I wasn’t impressed by those, but nonetheless, they’re nice to have. If you don’t have access to a second guitar, you can put in a cheat code that will unlock all of the songs for you.

There is a difference between unlocking songs and buying songs. You collect money by playing the career modes. With the money, you can by additional songs in the store. These are not “unlocked” songs per se. You cannot buy songs that need to be unlocked, and I described how to unlock them above. You unlock one song per concert section.

Just my two cents…I’ve spent way too much time with Guitar Hero lately…