I've noticed that with food smells after scrubbing out refrigerator dishes with dish soap several times. So my two-bit theory is that, sure, tiny traces of the former contents of a jar may still carry a scent. You can air the jar and wash it some more, by hand, with a good dish brush, and eventually the ghost may fade. My suspicion is that your nose is more sensitive than the new tobacco will be, and that you won't compromise the new tobacco by putting it in a jar where the previous blend is faintly detectable. Only a blend that would be of concern in a pipe bowl, like the Lakeland blends, might be of further concern. What is really important is to make sure the jar is, in fact, thoroughly washed with ample dish soap and then rinsed thoroughly, but most of all, dried really well. After that, I think you are wasting your time trying to exorcise every last sniff's worth of scent from the previous leaf.