Christopher, Mikes staves are usually pretty fresh when you get them. He goes through so much wood it hardly has time to dry much less season. At last years Classic Mike gave me a 2" diameter osage pole that was cut the year before. After I had it at home for a few months I cut it in half on my bandsaw. It wasn't completely dry inside. I bound the halves together with spacers between and let them rest for another 6 or more months before untieing them. That was a month or so ago and I'm still not ready to use either one of them yet.
Two year ago I bought a stave from Mike's Dad at the Hickory, NC shoot. It had been cut a month before. I reduced the stave to 3 staves(one pretty slim) and within a month made a 60" static recurve. The wood felt dry and even sounded dry under tools so I completed the bow. After a month or so I noticed frets. I'm sure it was the dry but unseasoned wood that caused the frets.
An extreme example of humidity effecting wood bows is a sinew backed hickory bow I made, copying Jay Massey's Medicine Bow. Like I said sinew backed hickory plus it has rawhide over the sinew. When I made the bow it pulled 56#@26". A month later in our humid summer weather it dropped to 45#@26". I sent the bow out to Kenneth(Little John) in Colorado and within a month it was at about 65#. That is a 20# difference over a few months. Granted all of the ingrediences of this bow, hickory, hide glue, sinew and rawhide are all very hygroscopic, meaning they take on and release moisture as the humidity changes.
I also covered a well seasoned osage bow with snake skins using TBIII a few years ago and the weight dropped about 10# when I thought the backing was dry. A month later it was back up to weight.