The year on the label records a growing season: how much rain fell and when, how warm it was, whether disease pressure was high, and whether the fruit could be picked at the moment the grower wanted rather than the moment the weather allowed.
Where it matters most
In marginal climates near the edge of reliable ripening — Burgundy, Bordeaux, Champagne, Germany's river valleys — where a difficult season is genuinely difficult and the spread between years is wide. In consistently warm regions the year-to-year variation is much narrower, and vintage is correspondingly less informative.
Non-vintage is a choice
Most Champagne and many fortified wines are blended across years on purpose, so that a house style stays constant regardless of what any single season did. NV is a deliberate strategy, not a lesser category, and blending across years is the specific tool that makes it possible.
The trouble with vintage charts
A chart compresses a whole region into one number for one year. Within any vintage the difference between producers is routinely larger than the difference between vintages, so a chart is a weak signal applied confidently.