Exactly.
WHERE is the hard evidence about the characteristics of the ash cloud as it developed (locations AND particle sizes AND densities per cubic metre - yes - you need ALL of these to come to a valid conclusion about safe routes to fly.
As far as I can tell, if you discount freelance flights by operators which were as much to do with
PR as scientific data collection, there was very little extra data collected over and above what was available on 14/4/10. OK - the computer models might have been tweaked but there was (apparently) very little REAL data collection going on in UK, apart from redeploying some cloudbase LIDARs and a few flights by D-CALM and ???. How effective upward-pointing LIDARs are at collecting specific ash data for the different flight levels immediately above, I don't know. Nor how many and where they are. Especially at high ash levels, I don't see how upward-firing LIDARs could cover all the flight levels anyway: 'particles hiding behind other particles' problem.