I no longer bother trying to stay at O'Cebreiro. For me it is simply not worth the hassle. There are nowhere near the number of rooms available that are needed, from April though September. This is a very popular place and there is no sign that additional bed space will open up any time soon. Also, the Xunta albergue there has seen better days. It is fine in a pinch, if you arrive in time and there is space, but, this place too is over-subscribed.
I stay before or after O'Cebreiro in pre-reserved rooms. On occasion I stay before O'Cebreiro at the Vega de Valcarce truck stop hotel. It is a secret value, and one I highly recommend if you have not tried it. Huge inexpensive rooms, laundry facilities on site, and just across the river from the main route.
Depending on the weather, the next day, I either walk up, over, and beyond O'Cebreiro, or, if the weather is adverse, I will taxi to O'Cebreiro to avoid the hazardous mud slog walking uphill from the valley. Once you are on top of the hill at O'Cebreiro, making Tricastela that day is no problem, plus it is mostly downhill...
This is just one person's opinion... If you have a secret to finding advance booking for a room at O'Cebreiro, go for it. I still stop in for coffee, and lunch or breakfast, but I no longer linger there. Once was enough. if they want my custom, they will create more rooms... THAT is going to become the problem along the length of the
Camino Frances as the numbers grow each year.
I hope this helps the dialog. You are free to disagree with my approach to this housing shortage, but I refuse to be a victim. So, I vote with my feet, literally...