Why aren't FM's recordings in tune?

[CarneVaca]

Not knowing how to read music or having no formal training has nothing to do with what keys you choose. Keys are all about tone and what works with your voice. So Lindsey picks up his guitar, probably tunes it to standard tuning most of the time, maybe clamps a capo somewhere up the neck and goes for it. Or if he's feeling adventurous, he might retune to drop D or whatever. Interestingly, in Guitar World Acoustic, there was a transcription of Peacekeeper. And in it, I believe the transcriber said to tune slightly flat from Gm.

The original Peackeeper was in Em. Lindsey changed keys probably to fit Stevie's voice. I can't recall, but he probably clamped a capo on, and unfortunately, capos detune your guitar ever so slightly. Usually, everything goes a little sharp. Sometimes a little flat. Rarely does the pitch remain perfect.

That may explain some songs, but not all. Sometimes studio trickery may change the pitch somewhat. Let's say Lindsey decided to slow down peacekeeper on tape. I don't know if that happened, but it's possible. That slightly flat key would have been one of the results of slowing down.