When have the polls been wrong? The polls have been pretty damn accurate every time. Any electoral differences within the margin of error or due to some institutional technicalities. You’ll need something truly extreme to shift the trends, otherwise this is the likely outcome. The only instance of this that I remember is the Canadian conservatives were poised to win a landslides because Canada universally hated Trudeau, but then Trump threatened to invade and annex Canada and that caused a change in the voters. I don’t forsee something like that happening in Spain.