Mold spores are everywhere. What mostly determines growth is moisture content and temperature. Keep your stuff on the dryer side, keep it as cool as possible and you greatly lower the chance for mold growth. Your cellar should be dry. If bought in tins, you have the choice of opening, checking and altering as needed, then moving to jars. At least with jars you can "look in." As to the dangers of mold, some molds can produce highly potent toxins. Rye mold (ergot fungus) causes hallucinations and severe bodily effects. That is where LSD comes from. It only takes a few dozen micrograms of ergotomine tartrate to give you a "trip." I would take mold seriously. If you find moldy tobacco, throw it out, unless someone possitively determines that the fungus on tobacco is fairly benign. Anything with a strong blue or green or red color, that is a sign of it being very dangerous. Chances are that even in other parts of the jar/container not visibly affected, the spores are present there as well. You are playing with fire handling or smoking anything that has been contaminated by mold. Your best bet is to keep small quantities in individual containers so that if contaminated, you risk losing little, and if one jar goes bad in a blend, that is a good sign to open all the others, inspect them and let them dry out a bit.