Hi Chris,
Many pilgrims will remember that wonderful 90 year old woman (Felisa) who had a ramshackle stall on the side of the road just outside Logrono with a sign that read: Higos-Agua y Amor (Figs - water and love) and, of course a sellos (stamp).
Felisa died on 21 October 2002 and a little bit of the charm of the camino died with her.
You can have your passport stamped at refuges, cafe-bars, churches, museums, town halls, tourist offices, hotels, inns etc. This means that you can collect many stamps every day - and, they are all valid - they do not have to be stamped by the refuge.
In 2002 I filled up two credentials with beautiful stamps and I am prud of all them. When I handed it in at the Pilgrim's Office, there were so many stamps that there was little doubt that I had walked the entire distance from Roncesvalles to Santiago!
So dear pilgrim, enjoy those special occasions when you can stay in a hotel (sheets! private loo! pillows!).
Sil