I usually obtain a stamp on the inside front cover, to START my Camino, at the Cathedral, Church or Pilgrim Office located at my starting point. This Wednesday, that will be the Cathedral Se at Lisbon. Then, at Santiago, the Pilgrim Office affixes a Cathedral stamp to CLOSE that credencial, and Camino.
But, as said above, for purposes of documenting your Camino, to establish distance walked for the Compostela, any stamp from the first place you started is sufficient.
I hope this helps.