Two examples I can think of:
I discovered the band The Verve Pipe after hearing The Verve's Bittersweet Symphony and searching for more of their music. I got The Verve Pipe's The Freshman, loved that, and listened to music from both bands for weeks, if not months, before realizing they were actually different.
Similarly, I had an MP3 of Guster's Parachute mistagged as Coldplay's Parachute for about five years, and thought it was weird that it sounded so different from the rest of the Coldplay album. Took me forever to figure it out. I like Guster a lot more than Coldplay.