I've been working for some time on a kind of primer on "getting to know fragrance notes" (or at least, what little I know on the subject). I kept stumbling over the need to debunk some of the common fallacies about the "lists of notes" that are associated with any given fragrance, and I finally gave up and decided to tackle that topic first.
Everything below can be neatly summed up as follows: not everything in a fragrance is necessarily in the list of notes, and not everything in the list of notes is necessarily in the fragrance. There, now I've saved you the trouble of further reading.
What are lists of fragrance notes, and where do they come from
The lists of fragrance notes you see here and there on the internet are usually provided by the public relations department of the perfume house in question. They are meant to give some general idea of what the fragrance "contains", or at least, what the PR department thinks it smells like (or perhaps more accurately, what they think describes it most alluringly to potential customers), but that is all. They aren't recipes, and they aren't complete. Sometimes they are very short and sweet. For example, the recently released Ungaro by Ungaro lists only 3 notes: jasmine, saffron and amber. In contrast, Shiseido's recently re-launched Zen fragrance lists 20: grapefruit, bergamot, peach, pineapple, blue rose, freesia, gardenia, red apple, violet, lily of the valley, hyacinth, rose, lotus flower, patchouli, cedar, musk, white musk, amber, incense and marine plant. There is no reason whatsoever to think that Zen actually contains more separate ingredients than Ungaro. It might, but then again, it might not. Perhaps both fragrances contain exactly 101 "ingredients". As consumers, we will never know (and speaking for myself, I couldn't care less).
Moreover, the "list" might get tweaked between the time it is first announced and the time you read it on a department store website even if the juice itself hasn't changed in the interim. Or, the PR department might give one list to the sales associates in the stores, another list to the press. This leads to many misunderstandings. From time to time, you'll see a post on a fragrance forum saying "Site X lists these notes for Perfume Y, Site Z lists these other notes, which is correct?" The best answer is neither, either, both. That is, neither is a complete list, either might be a better representation of what the scent "has in it". Take your pick, or combine them, it doesn't much matter.
Correspondingly, when you know a fragrance has been reformulated and you see a "new" list of notes, the difference between the old list and the new list may not have anything to do with how the fragrance has actually changed. It may simply reflect changes in how the PR department wants the fragrance to be represented to the public. It is not likely, after all, that you will be told that the expensive Grasse jasmine in the original has been replaced with a cheaper jasmine from elsewhere or that part or all of it has been replaced by an even cheaper synthetic jasmine. Nor will they alarm you by informing you that the synthetic musk in the original, which is now banned, has been replaced with something safer.
Why the list of notes doesn't matter
First of all, as we've already alluded to above, they don't tell you everything that is in the juice. Another common forum post goes "I hate aldehydes, what fragrances don't have any aldehydes?" Then people list all the scents that don't have "aldehydes" listed in the notes. This is not how it works. There are all kinds of fragrances with aldehydes that don't list aldehydes as a note (and, there is more than one kind of aldehyde — you might like one and not the other, and they might only bother you in high doses). There are also many fragrances where the aldehyde is "listed" as the note it is meant to mimic, for instance, if you see "peach" in the list of notes, what you might be smelling as "peach" could be an aldehyde.
Even if a note is listed, you don't know what specific aroma chemical was used for that note. So, for instance, I also see posts that say "Musk always turns sour on me, what fragrances don't have musk?" (and then, as you can guess, people list fragrances that don't have "musk" in the notes). Two important points: fragrances without any synthetic musk are rare, and there are many different aroma chemicals meant to mimic "musk". There are woody musks, fruity musks, powdery musks, clean musks, "metallic" musks...the list goes on and on. One fragrance might have one of them, another might have another, many perfumers use more than one in the same fragrance. The word "musk" in a list of notes therefore doesn't tell you anything about what it will smell like, and there is no reason to assume that because one fragrance with musk smelled sour to you that another one necessarily will.
The same holds true for many other notes. Take almost any floral note — tuberose, jasmine, rose, whatever. The fact that the flower is in the list of notes doesn't mean any actual flowers were used in the making of the perfume. There might be "real" jasmine, there might be a combination of synthetic and real jasmine, there might be synthetic jasmine only, there might be a combination of several different synthetic jasmines. There might be a synthetic aroma chemical that smells like "flowers", and they've decided to list it as "jasmine". So, as with musk, you might like "jasmine" in one fragrance but not in another, or you might see jasmine in a list of notes but not smell anything like jasmine in the juice, or you might smell jasmine in the juice, but it isn't in the list of notes at all.
In some cases, perfumers use what we might call "re-engineered" aroma materials. For Hermès Brin de Reglisse, perfumer Jean-Claude Ellena "...turned to his colleagues at an independent perfume lab in Grasse. He asked them to slice natural lavender into 50 distinct groups of molecules, sniffed them all, discarded five and reassembled it" to get the exact "lavender" he wanted. Likewise, the patchouli used in perfumes these days is often processed to remove the heavy earthy undertones that render it too "hippie-ish" for modern consumers. Many people who don't like "patchouli" (including me) may find they barely notice patchouli in newer fragrances, others (again, including me) find the use of all these smoothed-over natural materials has rendered many modern perfumes too clean for comfort.
You should also be aware that there are aroma chemicals that smell like more than one "note", and these may be listed in the notes as separate entities. The notes "precious woods, amber and musk" could all come from one single synthetic aroma chemical. Another company might use that very same aroma chemical and just list it as "musk", or "sensual musk", yet another might list it as "exotic woods". The notes "tuberose, orange blossom" could come from one aroma chemical, so could the notes "mimosa, jasmine" or "leather, cedar, vetiver".
One final note that seems to cause confusion is amber. After the release of Prada Amber Pour Homme, I saw people express surprise that the list of notes (bergamot, mandarin, neroli, cardamom, geranium, vetiver, orange blossom, myrrh, nirvanolide musk, labdanum, sandalwood, tonka bean, vanilla, saffron, patchouli and leather) did not include "amber". There is no single natural material called amber; it is a cocktail of notes (or an "accord") that might include labdanum, benzoin, vanilla, tonka bean or patchouli, just to name a few possibilities. A fragrance might contain one or more of those materials, or it might just contain a synthetic note that smells "amber-y", and the perfume house might choose to list the individual notes, or just say "amber", "molten amber", "hot liquid amber", or whatever they think sounds good.
Why the list of notes does matter
You might wonder why you should bother reading the list of notes at all, then? Well, my answer is simple: as a consumer, it is about all I have to go on*. There are 2-3 new fragrances being released every day, and I'm not planning to smell them all. And while to some extent the list of notes is fantastical, it can offer clues to consumers who are trying to figure out what is worth the effort of smelling.
The "sparkling green freshness" listed in the notes for Gwen Stefani L.A.M.B. L made me suspect that the top notes would remind me of air freshener, and lo and behold, they do. I can smell the pear and the sweet pea in L, as advertised, even if there aren't any "real" pears or sweet peas in the juice. Likewise, the "strawberry sorbet" and "caramel popcorn" in Christian Dior's Miss Dior Chérie were pretty good clues that the final result would be sweet and fruity, and it was, same goes for the "red lychee, golden quince, kiwi and cupcake accord" in Britney Spears Fantasy.
I can think of plenty of examples where the list of notes has led me astray, and certainly it never tells you everything you need to know. This list sounds lovely to me: green ivy, tangerine, water lily, orange flower petals, Moroccan rose, jasmine sambac, mimosa, apricot skin, amber, precious woods and musk, but it's for the upcoming Vera Wang Flower Princess, and having already smelled the original Vera Wang Princess, I'm fairly sure Flower Princess won't be joining my collection.
So, make what you will of lists of notes, but don't forget to trust your nose. If you smell vanilla but it isn't in the list, don't assume that means you're dreaming, and if the list includes vanilla and you can't smell it, don't worry that your sense of smell is to blame.
* And mind you, I'm not complaining. I'd much rather read (and wear) "lily of the valley" and "musk" than hydroxycitronellal and galaxolide.
Note: images, top left to right, are ~
Lavender [cropped] by Thowra_uk at flickr; some rights reserved.
Blue Atlas Cedar [cropped] by J And R Photography at flickr; some rights reserved.
Yuzu citrus [cropped] by alde at flickr; some rights reserved.