I freely admit to being ignorant of most of the radiation discussion. I'm slightly tempted to try explaining averages to Simon, though, to see if he can understand why "this is the average" necessarily proves that some data will fall below, possibly even significantly below, the stated figure.
There are several issues going on with the data, and they need to be addressed in some sort of order.
The CRaTER data actually show the complexity of the issue, as the data for the GCR background falls with increasing solar activity, therefore citing an average is utter nonsense.
The CRaTER data very clearly shows that the GCR flux varies significantly about an average.
The next point, which we have not got onto yet, is that the detectors all give different values. So even if we did have CRaTER type data for the missions, could we necessarily compare the data from an orbiting satellite with dosimeter data taken from the CSM and the astronauts. Not all methods of measuring dose are the same.
The argument presented is erroneous given the complexity of the problem, not only from the point of view of the complex nature of space radiation, but measurement theory.
The discussion, why appearing trivial and semantic based, really shows evidence of this claimant's lack of understanding. The log scale might seem trivial to the outsider, but it's actually the source of why the claimant is wrong.
Apologies if you knew all of the above.