Well, this is a later picture. Note the zero vis available, yet there's a 4x5x4 block of infused vis just sitting there, untouched. The node is actually pulling vis from another node first.
I drained the close node to zero with the mirrors and two more up the chain to zero and only one vis ore changed to dull. Now, I don't know how many "natural" ones converted - I should have been working on a flat creative instead of a normal worldgen - but was surprised they didn't _all_ turn dull