It is possible, the spalting (as you most likely know) stems from mineral streaks in the wood, so what you have is some decomposition by fungi and loss of wood, but still have the minerals deposited throughout the wood that remains.
The knotty sections may be due to resins in the woods. "Knots" in boards typically weep sap, and for years later too. So that could account for the extra ash possibly. Another thought is that the wood is denser in a knot.
As a woodworker though, it almost seems sad you are burning spalted wood. What great projects can be made from them, assuming they are not past prime. But I understand the need to stay warm too.
As a side note, did you hear why the piece of spalted pine
firewood was dating the hot, bombshell blonde? Well its obvious, he was a Fungi (fun guy)!!
