I forgot about this until the other day. I wrote and recorded a string arrangement for someone in the wrong key.
When MuteMath was working on their Armistice album, they asked me to write some string parts for several different songs. Several of those made it on to the album, but there was one that didn't. As I recall, I was getting ready to leave on tour with Sleeping At Last when Darren (MuteMath) called me. They were in a bit of a time crunch, but needed some string ideas tracked for a song. They hadn't tracked much of the song yet, mainly just drums and a little bit of bass. I was told to "just run with it". I only had one night to try to knock it out, so I had to make it count. I stayed up all night working on ideas and left for the tour the next day. I sent what I had to Darren, and basically told him, "This will have to work, because I'm gonna be gone for the next three weeks".
The next day, I was riding in the van when Darren called me. He asked, "What key did you record those parts in?". I said, "I tracked everything in E, just like the song." He said, "The song is in A...". I just sat there in silence, trying to wrap my head around it. How could this happen?!? Pretty simple actually. And you may need to know a little music theory to understand.
The song only had bass and drums, and the bass was pretty much playing only the root notes of the chord. So there are certain progressions that work in both E, and A, with minor variations. For instance, if the chord progression is A, E, B, E, it works in either key- EXCEPT for the B chord. In the key of E, the B is major, in the key of A the B is minor. It's amazing to me that moving one note, one half step in either direction can completely change the entire song.
That is how I recorded an entire string arrangement in the wrong key.