Hellmanns may disagree with me but there are a couple of stages in making these things.
At least the way we did it.
You can but dont have to work a lot of it green and the ends can be sealed up with tar to help stop checking or splitting on the ends.
One important thing is to have the wood completely dry before you do the finale fitting.
I have been known to put things in the oven to do this.
Or at least bring them in the house.
Then when the handle is fitted humidity can set in and make it swell up and it will be as tight as the devil.
The split in the end is for hard wood wedges you drive in.
This is the reason you cant get a good hardwood floor installed hardly any more.
The HOA's have rules that state a house has to be finish in a certain amount of time.
This is just about the amount of time it takes the flooring to acclimate.
But you cant have that wood sitting in the house while they are putting up dry wall and taping and floating.
Some of this depends greatly on the type of wood too.
Wood is a living thing that swells and shrinks once you understand this it is one heck of a lot easier to work with and make a good product.
Worth.