What's in a blend

[sgutte]

I like to know what I'm drinking. Recently I enjoyed a 1999 Duca di Salaparuta, Terre D'Agala. In my research I found that it was made from Nerello Mascalese and Merlo, but until 1998 it was made from Nero d'Avola, Perricone and Frappato.
Is this common that the same label should change so much? I would expect they would change the name.