You obviously haven't read the thread thoroughly and certainly not my own post
#2486.
The trouble with 'careful reading' of anything is that it can STILL be selective!
The stated reason why the track of the NASA DC-8 blundered into the ash (which was part of a cloud well-known to the VAAC) was that it was 'old' so that the ash particles had become ice-coated. The satellite imagery therefore mis-identified it as normal cirrus.
So: had the flight been in daylight, there would be another question. What would the pilots have actually seen above them, 'obscuring the stars', or around them? Brownish ash or whitish cirrus? You tell me! After this length of time, I doubt there's any daytime visual evidence of what the cloud looked like at the point where the incident occurred but there might not have been much to indicate 'Here be Ash'!