What can happen is; If the prop is torqued when the humidity is dry and later the humidity increases, a wood prop will swell somewhat. This can, and has, caused the prop bolts to stretch and in extreme cases break.
It is pretty obvious when the bolts stretch. You can see it at the base of the threaded portion of the bolt.
I brought this up at an EAA presentation once and one of the guys went home and checked the prop bolts on his Hiper-Bype. He found that they were all stretched and one was actually broken.
I just found a picture of a stretched prop bolt that I have.
I don't do pictures here but if someone will give me an email address, I'll send it to you and you can post it.