Does that change the math above if they're tied into the grid?

If they're tied directly to the renewables (Meta is doing this in some places), then true, not a technical increase. But you could still maybe claim they're instead preventing the equivalent reduction on average/grid (and, say, decommission of some of that coal). I suppose that's a separate point.

If it’s truly separated (no interconnect agreement) or generation capacity is below 1 MW, it won’t show up in EIA data, yes. Rooftop solar is also not included in the data for that reason.