I would rule that unless the toxin has been combined with DMSO - thus making it a contact poison (or a contact poison as well) - that if the armor converted it to Stun, yes, there was no penetration. I might - depending on the situation - rule that if the character didn't take any Physical damage at all, there was no penetration, but that's tough to make a blanket rule for. An edge is going to cut and deliver the toxin, even if it was just a scratch to the troll or street sam, but an injection dart might not get enough purchase to do so.