I am not trying to sound like a jerk but depending on where you are talking about the pilgrim level can be very different. From Irun to Bilbao or Bilbao to Santander I am sure is way different than later on in the Camino, after the split to Oviedo. Many choose to go to the Primitivo. It will be much quieter after that until you get to around Abadin when you are getting close to the 100k mark and it gets more crowded again. It is usually the busiest the first few days out of Irun. As is the case out if SJPP. Things will usually open more as pilgrims spread out, I am sure others will answer you and I would think if you are starting in Irun the hospitalero at the municipal in Irun can give you a good idea.
Then there is the tourism factor. The north coast of Spain is full of tourists this time of year, surfers also. Many of the surfers camp and stay in albergues that are not pilgrim only. Prices will be higher also because it is tourist season. I am not sure when things change but I am sure once school begins tourism recedes. When I walked, granted it was 5 years ago, and I started about 6 weeks later than now, the most crowded was between Irun and Bilbao.