Yes I agree living things like bacteria/yeast cultures are hard to get right. In regards to your previous example you can get the blend of leaves right, but if the plants aren't genetically identical or even aren't grown in the exact same climate the end product may taste very different. When it comes to completely artificial flavorings though it would seem to me that it would be much simpler. For example isoamyl acetate is isoamyl acetate regardless of where or how it is produced.