> I agree it would be best to stay current [...] I am concerned > that such a change could potentially break existing > software which might depend on certain values.
Yeah, I agree that it is a problem, but in the end the old numbers need to be seen as a bug, and putting the newer numbers as a bug fix. Regression tests often go bit-by-bit instead of allowing for a certain tolerance (an example of this is TeX's famous test suite), but when those tests break the authors can look at the GSL release notes, and update their ground truth to the new values. This is the same thing people have to do with bit-by-bit regression tests when "non-physical-constant" bugs get fixed. And of course there's an xkcd: https://xkcd.com/1172/
