It's still a great mystery to me where the VA evidence is going!
Under present (new) rules, it would be very unusual for an engine to run for as long as an hour in an ash zone or around the edges where it can be assumed there would have to be some ingestion. Nevertheless, if the permitted worst case is 10 (TEN) kilos per hour through the front of the engine, there would have to be some traces left, somewhere, from shorter encounters.
So where is it??
Or are people not yet looking in the right places?
Not much unique about volcanic ash particles other than their melting points compared to surface dirt. So with all the sucking of engines for years on-the-wing, not much accumulations are found within the engine. The coarse stuff hugs the outer walls and goes out the rear after slowly eroding blades. The fine stuff flows freely through the cooling holes and finally ends up out the rear of the engine. The in-between stuff either dirt or ash may get stuck in the cooling holes and result in some annomally in a single engine some day.
Lots of data available to the big operators to put this in perspective so ask them.