Yep, wind shakes can be darker colored if they've been there a while.
Drying checks can occur on the sides of a stave. I've seen what you've shown in your pictures develop from drying osage staves too fast, and especially if drying them with the bark and sapwood still on.
In one instance, I'm confident they weren't wind shakes because a friend and I cut a tree and divied up the staves, the ones I brought home and seasoned slowly were fine. The ones he took home ALL developed side checks. Turns out he left the bark and sapwood on and put them in his brand new wood shop, which he built upstairs above his garage. The garage unfortunately, he keeps heated with a wood burner directly underneith. It's like a kiln up there.
He gave me the remaining staves, hoping I could do something with them, which I did. I burned them... in MY woodburner
Other than those checks, they were some of the nicest osage staves I've ever seen. Very disappointing.
How was your stave cared for? And at what point in construction did they appear?