Check out the difference between "supplemental" and "supplementary" grounding electrodes
It's in 250.53(D)(2) and 250.54.
A supplemental electrode is a required electrode.
A supplementary electrode is one that "shall be permitted", and isn't subject to the same requirements
See if that doesn't help.
Also, one of the moderators told me the other night on the chat that the idea behind static discharge was to get the static to the closest grounding plane (not airplane).
