As Joan states is the way it is done. If you think about it, the grapes are grown and harvested. As soon as they are harvested they are crushed and pressed and made into wine. This happens in one season so you use the year of the harvest.The same plot of ground can produce different quality grapes from year to year due to weather and other factors. Notice that certain brands make the same type wine every year but some years the wine is much more expensive due to perfect grapes that year in sugar content, acidity, etc. that produces a superior wine. Appellation or Terrior regulations require these labeling laws to advise the consumer of the quality of the particular wine. Of course poor winemaking practices can produce a sub par wine with superior grapes but you get the picture. As stated, home winemakers aren't required to abide by labeling laws.