On iTunes, I have 1 song on 2 different albums...?

Last year, I went on iTunes and downloaded "Now That's What I Call Music!" Volumes 38 and 39 (I live in the U.S.) and both albums have Hot Chelle Rae's "Tonight Tonight". However, I downloaded one album after the other and after downloading, that song only appeared on one of the albums. I didn't expect this, but I figured that iTunes just does that so the user does not have duplicates.

A few weeks ago I went on iTunes and I downloaded "NOW That's What I Call Music!: 10th Anniversary". One of the songs on the album is "Lollipop" by Lil Wayne. But I downloaded NOW 28 tonight and it also has that song. I was hoping that it would do the same thing where it avoids giving me a duplicate, but it didn't, so now I have 2 copies of "Lollipop". I know that I can just delete one of them, but I wouldn't like to have "missing" tracks on either album. Is there a way that I can make one of them correspond and automatically play with each album's sequence and then delete the other one? I guess it doesn't really matter but I'm a little strange about my iTunes storage haha.