That early version of Brown Eyes has the lyrics--
If you're even feeling lonely
You can always call on me
Through all the years I've known you
You've always been good to me
Yesterday's tears
You're over the sad years
I want you to know I'll always be there
My view is that Christine wrote the lyrics inspired by Peter Green.
And we know that, with few exceptions, Chris wrote songs on an as-needed basis.
So it makes sense to me that the original idea (probably Mick's) was to have Peter Green play on a track, either in the studio or (perhaps more likely) using an existing recording, based on a Christine instrumental demo (a'la Butter Cookie), and then Christine wrote lyrics to match the purpose.
But for whatever reason (the weak lyrics? issues with Greeny's rights? Lindsey's preference to shake off the pre-Rumours associations?), the song was heavily reworked once it got in Lindsey's hands.
https://www.youtube.com/watch?v=e7AYuSW6sDg
That's my theory anyway.