Townies will only want to use stored materials, even if they can't be reached and there's others that can be.
I accidentally deleted my main ladder in the middle of my town. I ordered another one to replace it and waited a few minutes, but no one ever took up the order, even though it was top priority (I assume it's under item creation). I also had a fence being built around my graveyard, but no one was doing it. I checked my tree farm at the edge of town, it had lots of wood laying on the ground around it, but no one was taking it, they only wanted the wood stored in the barrels in the currently inaccessible underground storage area.
Luckily (well, kind of), I had dug down in another area and it still had a ladder, so I ordered the townspeople to mine over to the main storage area. That took a while, but when they did it, they grabbed the wood out of the barrels and started making the fence again, and eventually the ladder too.
I really only wanted to see if that was the problem, I had to quit without saving because a few of my people died trying to build the fence and ladder, too long of a walk for them. But they did get back to work when the pathway was mined away.