Ever refer to a specific wine in that all-knowing, collective way? You know, like a wine that comes from a 40,000 case production, let's say Chateau Margaux, and you find yourself saying, "Last time I tasted the '89 Margaux it was still tight." Or, "The '78 margaux is my favorite first growth of the vintage."
Even if one had tasted a dozen bottles or more, there still remains the question of bottle variation.
Especially as wines age, change hands, and move from cellar to cellar, things happen. Some bottles get special storage and others are made to suffer in less than ideal conditions. Those are only two of the many reasons that bottle variation occurs. The best wine tasters, in my opinion, are the ones who recognize that bottle variation is a fact of life and accept it. They even find education in it.

Bottles of wine from a specific production are like siblings. They have the same origin, but they might grow up completely differently. And depending on their "upbringing", they will have different characteristics later in life. Recently, I opened a bottle of 1990 Henriot Champagne with 3 other sommeliers. It is a great vintage from a fine house; the wine should have been magnificent. However, I found it mature, and both oxidative and slightly maderised. So did one other sommelier. The other two thought that the wine was fine, showing its complex maturity, toastiness, and richness. I didn't really care for it, but they did. I insisted on opening another bottle. Sure enough, it was bright and fresh. It was still rich and complex, but it lacked the "over mature" characteristics of the first bottle.
Bottle variation. It is as simple as that. Of course, it is hard to explain because both bottles of wine came from the same case and had lived their lives side by side. Strange. But I remain beholden to yet another of wine's great mysteries. Just when you think you've got it kind of figured out, fine wine does to us what nature intended-- it pleases us, enchantes us, disappoints us, bewilders us...
Wine is one of life's many wonders.