After reading the thread about how to pronounce the word "millésime" in French, I wrote a reply in which I mentioned that the word refers to a date, as on a monument or a coin.
Well, I began to think about this... Why would Creed use this term to name a perfume? So I did a little investigating. I've been looking at a book by Annick le Guérer, Le Parfum: des origines à nos jours (Odile Jacob: Paris, 2005, ISBN 2-7381-1670-1) and I decided to look up Creed in the chapter on niche houses. There (p. 281), she mentions the following:
"In order to take into account the variations in aroma of natural products whose characteristics are not identical from one year to the other, the House of Creed offers an innovation. As on the bottles of great wines, the year is inscribed on the flasks of its Millésimes — eaux de parfum composed of very rare and very costly essences — taken from two thousand specimens. 'A synthetic rose that you bought in 1990 or 1995 is the same, but a natural rose... well, that one changes... and then someone says to me, "But your perfume has changed!" One indicates the year so that the clients will not be surprised at these changes.' " (Translation mine).
So the "millésime" is the date on the flask that indicates the year of purchase of the key natural ingredients that went into the fragrance. Your 1995 rose may be greener, flatter, or spicier than 1990's rose crop was; therefore, you shouldn't be surprised that they don't smell the same. Creed is accounting for the yearly variation in natural products that it uses in its scents. I guess, like a wine connoisseur, you have to know that the grenache grapes in year X were fruitier than in year Y, and if you prefer fruitier grenaches, then you'd better buy the year X vintage bottles. If you live in Grasse, maybe you know what years the acacia flowers were really killer, and you'll look for one of those years on a Creed Aubépine Acacia. At least Creed has deniability if you say it wasn't the same as another year; but you can't expect Mother Nature to have the same consistency as IFF or Firmenich.
So, children, that's why they're called "mIllésimes," which I never knew until now... but perhaps you did...
Thank you Candide for highlighting same.