I just wanted to make Harmonix (and users) aware that there appears to have been a problem with Mama Tried when I bought the song as a single from the Music Store (on PS3). Even though it showed up as Mama Tried (RB3 version) both in the Music Store AND within the game, it appears that the version of the song that I actually downloaded when purchasing is the regular RB2 version.
What kind of threw me was the fact that the Music Store listing showed it as "Purchased" instead of "In Library," and I suspect that "Purchased" might refer to disc exports instead of singles downloaded as DLC.
I went ahead and bought the Country Megapack, since it's a pretty nice deal anyway and I like playing Country in Rock Band a lot more than I generally liked listening to it, and as soon as I did that, when I went to play the song again, it showed Mama Tried (RB3 version) as an entirely new song, and the one that I had played 5 or 6 times before to try to get it to show up for the goal didn't have (RB3 version) at the end anymore even though I'm positive it did before.
So something appears to be goofed up there. Whether it's on Sony's end or Harmonix's I can't speculate, but be wary of buying Mama Tried as a single until this is resolved. If you go ahead and get the Country Megapack or Going Country Pack 7, you shouldn't have this issue.
EDIT: Just to make this shorter and clearer, the basic problem appears to be that when you buy the single of Mama Tried (RB3 version) on the PS3 Music Store, it actually gives you the RB2 version which doesn't count for the Country Jamboree goal, even though it shows as the RB3 version in the title.