There is also one other thing to consider. A house that old is

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Moderator Post (s) for this thread: > Jumping to Confusions by homebild on 06/28/2009

probably built with a balloon frame. That means the wall studs go from the basement to the attic as one run. Firestops weren't normal back then either, so every wall cavity is probably open from the foundation to the attic. That leaves an awful lot of open air space for air currents to pull things from the basement to the attic.

When I rebuilt my 1908 Painted Lady Victorian I had to add fire stops to each bay from the basement to the attic. It's possible that your new attic vents have provided enough air flow to pull coal dust out of the basement and first floor wall cavities and spread it through out the house.

There are ways to help your problem, if the framing is the issue, but they aren't pretty or cheap. I was lucky, my plaster walls downstairs were shot anyway so I filled three dumpsters with trash and added 2X4 firestops in each bay, top and bottom. I had to cut them from 2X6s since the studs were REALLY 2X4. New wiring, new plumbing, new phone and computer cables in each room. Then insulation batts, foil covered foam board, and drywall. The rooms looked great and you could heat them with a candle. That was after 2 years without a vacation or a day off. And maybe $5,000 in material.