"Aside from a yearly ceremonial peek inside its vault, which can be unlocked only with three keys held by three different officials, the prototype goes unmolested for decades. Yet every 40 years or so, protocol requires that it be washed with alcohol, dried with a chamois cloth, given a steam bath, allowed to air dry, and then weighed against the freshly scrubbed national standards, all transported to France."

Sounds sensible and reliable. No issue with corrosion, infiltration of gasses or lint I guess. And what about the other standards? Who knows which is changing?

"Steiner argues, the watt balance, with its Planck constant, is “a better realization,” because his system is self-contained and replicable, whereas the Avogadro project spans several continents and relies on a single artifact. "

A non-reproducible result is not science. It doesn't matter how many zeroes are involved; its not actually a verifiable fact if there's only one experiment, right?