Yes, I think there is a potential pitfall in just looking at previously published values. There's a kind of "blind leading the blind" element to systematic errors-- one person makes a plausible assumption, and in the absence of any contrary evidence, everyone else follows along. At some point along the way, the nature of that assumption kind of gets lost to history, replaced by a source of systematic error that is easy to overlook. Perhaps one single systematic error would cause us to go back and recreate all of those same plotted results, changing nothing but that one assumption, and we would find they were all higher as a result. That's the concept of "systematic" error taken to the logical conclusion of being systematically applied by everyone. Perhaps Tim is saying there is no error source that is really that systematic over such a wide array of methods, I can't really speak to that-- I merely point out that such would be an essential piece of that type of argument.