I recorded and mixed an album for a band three years ago, and they just came to me a month or so ago saying that a few of their tracks were wanted for a film.

Great!

... a week later, they wanted an instrumental mix of two songs.

Okay, where did I stick those sessions...

... a few days after that, it turned out the producer wanted ALL of their songs. Instrumental.

I usually delete most of my sessions after that long of a time frame, but luckily I still had them kicking around.