The historical cases of IV charcoal are incomplete because they do not discuss the long term effects of the charcoal, they merely report on the outcome of infection. Where did the charcoal end up? Hence I do not see anything which contradicts the idea that IV charcoal would behave dissimilarly to the cases of lymphatic accumulation of a similar material. I think a more interesting question is whether this isolated incident of lymphatic accumulation of carbon black is more common than believed, or whether there is a normal excretion pathway that works for the majority of people. We know from the paper that there is a limited ability to tolerate IV charcoal, which may indicate a significant bottleneck in excretion or metabolism. Given all that, I don't see heavy metals as being particularly relevant.