Vega Sicilia Reserva Especial Blends

Does anyone know this?

Which years does Vega Sicilia put in it's blends or Reserva Especial wines? I have some 20 different releases (release 1978-2003) and was wondering what vintages they really contain. These last years the labels indicate the 2 or 3 years they use to make their blends but prior to the 2004 release the labels do not indicate anything execpt a date of release or a lotnumber.
Does anyone have this information or know where one can find more on this subject? Many thanks, Jochen