You do have to flavor test you TFA flavorings, and record your impressions on each one.
When flavor testing any juice, you are trying to identify initially the one or two primary flavorings, and one or two secondary flavorings in the mix, so you have to be familiar with your arsenal of flavorings. Your sense of smell is the first step, way before mixing. What does the juice to be copied smell like? What tobacco flavoring comes closest to matching that flavor? Next, what else can you smell, and/or taste? If you cannot find some of the flavorings by smell and taste, it's going to be hard to copy. I can generally identify three or flavorings by smell, perhaps another one or two with taste. I don't have to get it perfect, just in the ballpark. There are such things as smelling strips too, which do help a great deal. I use them all the time. I got them from TFA way back when, but I'm not sure if she still sells them, but they are readily available.
Put the juice to be copied on the flavor strip and let it waft in the air below your nose. Take it in and try and put a label on what you smell. See how many ingredients you can identify. Check those aromas against the aromas in your flavorings. You may or may not have a particular flavoring, but still may be able to identify it. As you identify each ingredient, write it down, and then return here to report your findings, and we'll take the next step, i.e., mixing and percentages. good luck!