errrr...in the interests of accuracy...
The NASA report includes reference detection by on-board scientific instruments of 'volcanic ash' but only by inference - I read it to mean that they ACTUALLY detected sulphur dioxide, which is also normally present in VA clouds but does NOT give any idication of ash density.
The chosen route for the flight was specifically intended to run to the north of a KNOWN ash cloud. The location information (from London VAAC??) was incorrect and the cloud was further north than thought. The reason for the error was partly due to the satellite imagery showing 'ice' clouds (ie. cirrus) rather than ash because ash particles had acted as nuclei for ice formation - so the satellite really was looking at a form of cirrus. It seems that once an ash cloud is 'old' and / or reaches a certain height, ash particles WILL get ice-coated and therefore difficult to positively identify.
Accurate detection of ash particle densities and drift rates of VA clouds therefore still seems to be a problem in the absence of research aircraft flying through them or very near to them. Covering that sort of area is probably infeasible. Hence my suggestions that there should be a far greater focus on post-flight inspections of ALL aircraft in affected regions to give a backstop check on where the ash is and where it's going as well as confirming the safe condition of the aircraft itself.