Somewhere along the way during my most recent camino, I read that the bookings sites typically assert that they have no spaces left at a number of places that appear lower down on the list they supply (creating a perception of general scarcity), and assert that few accommodations remain at the spot one is actively assessing. It encourages people to make the booking. Then, one arrives and frequently finds that the hostal, albergue, pension, etc. is not actually full at all.
I've never rebooked an albergue or refugio, but about once every 7 days I do seek a private room in some kind of accommodation. I use booking.com because even if it tacks on a premium, I can see easily that I have confirmation of exactly the product/service I was seeking; it's far easier than phoning (trying to hear, etc). But I ignore the assertions that my chosen sites have only one room left. I've seen the same assertion made for several days in a row without that last room disappearing.
Honestly, even for my most desired place to stay on my most recent trip (the Via de la Plata Spa in Astorga), I waited until I was 24 hours from destination to make the booking, and I would not consider doing a booking any further in advance than that. 6 months out?? No way. Practically speaking, there's too much that can prevent you from reaching a destination on the day you think you will. Many times I've ended up a day early or a day late to a place I'd provisionally marked on my calendar as an anticipated landing point.
This past summer, the provisional idea was that I would meet Spouse at Sahagún, but he had blisters and shin splints, so he slowed down, and I took the train to meet him at Fromistá. And our plan when we'd bought our flights was that I'd meet him in León. The original thoughts were days apart from the actuality. And that's why one does not try to book accommodations in advance on an intense walking trip.
Being prepared for Camino really requires letting go of the schedule (other than arrival and departure at the beginning and end of the journey, and I envy those who can have completely open-ended dates for returning home!
