It seems that artist and labels like to include bonus tracks on their albums on Spotify. It's still the same album, just with added content. They mostly seem to release the deluxe versions of the albums on Spotify.
You can go to the desktop client and try going to the album page (click on the title of the album) and see if there is another version of it available. If there is, you'll see a little button saying "x more releases" at the bottom of the tracklist.
I hope that helps, have a lovely day! 🙂
SebastyRock Star 18
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