Flip over any bottle of champagne and look at the fine print on the label. You’ll find two letters followed by a registration number. Most people ignore this. It’s the single most useful piece of information on the bottle. The Two-Letter Code That Changes Everything French law requires every champagne producer to print a classification code on the label. The main ones you’ll encounter: NM (Négociant-Manipulant) — A house that buys grapes from growers, then makes and sells champagne under its own name. Moët & Chandon, Veuve Clicquot, Krug, Bollinger. The famous names. NM houses control roughly 70% of all...