Realize that having a reservation does not afford any advantage during check-in. Check-in occurs based entirely on when you arrive. Arrive early in the day and you will not have any problem, whether you have a reservation or not. Arrive later in the afternoon and you can expect a long wait to check-in. Hopefully, you will be luckier than I was in April, when my check-in took over two hours.
There was only one person who could check people in. There were multiple volunteers keeping pilgrims from entering the office and overwhelming the check-in person. The check-in person dealt with those having a reservation and those not based on your arrival time, not your reservation status. Pilgrims did not know or had a difficult time understanding that they had to show their passports, credentials, and if the had a reservation, evidence of that reservation, plus needed to fill out a survey form prior to seeing the check-in person. Some did not, making the check-in process much slower than it needed to be. Since my docs were in order and I had prepaid (reservation) my time with the check-in person took under 5 minutes. Some took longer having to go retrieve passports or credentials or booking information. Not sure why there was only one check-in person.
So having a reservation may get you a better bed in a better section of the albergues but it confers no advantage in obtaining a timely check-in. If that is an important consideration to you you might want to investigate the private accommodations available or ensure that you arrive early in the afternoon.