I know that I seldom know where I will be staying even a day ahead. I don't know how firmly they committed, but I can understand how it is easy for plans to change. I personally try to manage expectations as follows. I generally email potential hosts well ahead and let them know that there is a possibility that I might stay with them, but that I seldom know when or if I will stay in a certain place more than a day ahead if even that. I ask if they are OK with short notice and if not how much notice they require. Then I put them on the list and while on tour play it by ear either giving the required notice or skipping them as a stop. If they require more than a days notice the latter is more likely. At the end of the trip I email everyone thanking them regardless of whether I stayed with them or not.