That is achievable - their results are based on a statistic of 16,000 events, so the the exponential blur may be reduced. I do not question their statistical analysis (I haven't checked it in details, but on the first sight it seems to be correct).
No. And that is my major point against that paper - they do not discuss those issues (except of GPS time synchronisation, to which they paid lots of attention, and geodetic measurements, they mentioned). And the numbers they present for various components of systematic errors seem to be much underestimated as for my intuitions. Some of the possible sources of systematic errors had not been even mentioned in the paper.