Unlike Burgundy and Bordeaux, where growers bottle a vintage wine each year, Champagne growers blend their annual output of wines into non-vintage bottlings. They only "declare" a vintage wine in an especially good year (like 1923). Vintage champagnes are highly prized, and growers keep them off the market until prices are right. There is no way a 1923 Champagne would be in a restaurant in 1923.