One thing I really want to get into is the 1967–68 Save Star Trek campaign, because the more we research it the more all over the place the supposed numbers of letters are. GR is the worst, and the numbers he cites jump up and down willy nilly in various tellings, even as the thing was going on. And some fans of the era admit to having sent many letters, so the total individuals who wrote in is probably a fraction of whatever the total was.
