It really depends on the albergue. I have vividly memories of the albergue not only refusing to receive a backpack shipped ahead, but refusing to accommodate the pilgrims who had shipped it (this was in 2018).
My advice is only to ship your backpack to an albergue where you have a reservation and confirm what their policies are about accepting shipped backpacks when making the reservation.
I can't answer the questions about Pilbeo's list or daypacks, because I'm not aware of the list nor do I tend to ship my backpack. But generally, I would expect your daypack to include: valuables, water, snacks, first aid items, camera equipment (if you bring it), weather-related items (rain jacket if wet weather is threatened, sun hat if you don't always wear one, etc.). In general, the things you might want during the walk as opposed to at the end of the day when you arrive. If you are considering putting anything in your daypack that you think you might really need overall, not just during the walk, then you might as well make it your regular pack and not ship. Because you shouldn't be bringing anything with you that you don't think you will really need.