Covers you knew for years before you found out they didn't belong to the band you thought they did.

It took me years not to found out it was not original (after all the song says who wrote it), but to found out who originally record it:

Judas Priest - "Better By You, Better Than Me" (Spooky Tooth)
Iron Maiden - "King Of Twilight" (Nektar)
Cathedral - "Fire" (Arthur Brown)
 
I was reminded somewhat recently that Ace Frehley's "New York Groove" is a cover. Not sure if it just slipped my mind or I never knew?

Krokus' "Stayed Awake All Night" is another one I remember within the last couple years...

Non-metal-wise however, I just learned a few minutes ago that Heart's "What About Love" is indeed a cover.

Here's a few others that I've known for a very long time are covers, but I remember not being aware of that for a short period of time when I first heard them.

JP - Diamonds and Rust
JP - Green Manalishi
Queensryche - Gonna Get Close to You
Heathen - Set Me Free

Maybe 6 months ago a friend texted me a picture of his satellite radio screen which showed he was listening to Slade's "Cum on Feel the Noize" and asked me what that was all about.... He had no idea that the Quiet Riot version was a cover. Of course I had to tell him "Mama Weer all Crazee Now" was also a cover! :)
 
Heathen - Set Me Free

:)

A friend was crazy about this one when the video came out in MTV. He was into thrash but I didn't at the time, so I told him it was a Saxon cover and he was all bummed. Years after, I found it was Sweet cover in time LOL.
 
Kreator's cover of Tygers of Pan Tang's Gangland, the original is bad but Kreator's is so good! I always knew it was a cover but not by who til years later.
 
Kreator's cover of Tygers of Pan Tang's Gangland, the original is bad but Kreator's is so good! I always knew it was a cover but not by who til years later.

Strange, the EP (the CD version) says 'Gangland' it is a TOPT cover. I like the Kreator version a lot (I knew it first back in the day), but the original (which I bought several, several years after) is very good. one of the best albums by the English outfit.

Kreator-Out_Of_The_Dark_Into_The_Light-Cd.jpg
 
Black Sabbath - Evil Woman (Crow)
Black Sabbath - Warning (Aynsley Dunbar Retaliation)
Joan Jett and the Blackhearts - I Love Rock 'n' Roll (Arrows)
The Runaways - Rock & Roll (Velvet Underground)
 
There are A LOT of covers I wasn't aware of over the years, but two I've been listening to for years that I only just learned were covers are:
April Wine - Sign of the Gypsy Queen (Lawrence Hud)
Bon Jovi - She Don't Know Me (Fair Warning)
 
I knew that Messiah's version of Dreams of Eschaton (from Rotten Perish album) was a cover, but took me ages to find out who did it originally (pre-internet info was more difficult to get you know! ;)) Also Solitude Aeturnus - Deathwish, was a Christian Death cover. Always thought that it was a cover, but no info on the inlay card saying that it was a cover.