Herbs and the Senses
Human senses, especially sense of smell, are often much more sensitive than routine chemical analysis--so a barely measurable trace of one substance can have a disproportionate effect on the way we perceive it. The compounds responsible for the fragrance of Pandanus, for example, are present in amounts smaller than one part per billion.
While some compounds are so powerful, others require thousands of times the dosage, just to be detectable. Consequently, mere quantitative analysis can be misleading.
Sometimes, the combination of hundreds of trace compounds are involved in our perception of the taste/scent profile of an herb or spice. Vanilla and Ginger are perfect examples.
The components of these taste/scent profiles are not equally volatile. When these plant materials dry or age, different compounds are lost at different rates, causing the herb/spice not merely to lose strength but to alter its taste/scent profile. Fresh Tarragon, for instance, has an Anise-like aroma that is practically absent after drying, while a hay-like scent develops during the drying process.
Plants harvested at different stages of their development, or grown in different environments, or in different years, often have significantly different taste/scent profiles. Wine tasters are well aware of differences in the scent of wines from different microclimates and terroirs--sometimes only a hundred yards apart. The same variability exists for herbs and spices. It is the reason why Tellicherry Black Pepper is often preferred over other sources of Piper nigrum. Chile peppers grown, in the same garden, will contain much greater levels of Capsaicin if the plants are stressed by water shortages at certain stages of their growth.
Consequently, the provided chemical profiles should be used merely as starting points, not as definitive analyses. Wine experts spend their entire lives developing an understanding of the relationships between varietals, culture, climate and soil for just one species: Vitis vinifera. Don't expect the study of the thousands of species of herbs and spices to be an easier task.