My experience Sept/Oct 2017 for what its worth...
Took a light sleeping bag (650 gms) and a silk liner (80 gms). Used the sleeping bag in Roncesvalles albergue as it was cold and blankets not provided by the hostel.
Didn't need the bag again when I reached Burgos so I posted it home in the interest of reducing backpack weight. Didn't need it again until most of the way across the meseta when I stayed in another hostel that didn't provide blankets, so I put my long johns (thermals) on and slept OK .
Sleeping bag not packed for
Camino Frances 2018 (I leave in 4 hours)...
But then I do sleep hot...