July 22, 1966 is the hero, and it may be the single poster-richest day of the entire window: two core ballrooms, two iconic posters, one Friday night. At the Fillmore Auditorium, BG-18 - a Wes Wilson poster - carried the Association, Quicksilver Messenger Service, and the Grass Roots for a run of July 22-23. That run shifted on the second night, with the Grass Roots giving way to Sopwith Camel on the 23rd, a night that reportedly ran late enough to include an on-stage wedding around 1:12am Sunday. Across town at the Avalon, FD-17 - the Mouse and Kelley "Snake Lady" poster, one of the most recognizable images the scene produced - carried Jefferson Airplane and the Great Society for the same July 22-23 dates. The Great Society is the detail to sit with: this was Grace Slick's band, months before she left it to join the Airplane, so the two acts sharing the FD-17 bill are in a sense the before-and-after of the same voice. One honest caveat on the numbering: the BG-18 and FD-17 catalog numbers rest partly on browser-only registries, though they're dealer-corroborated, and the shows themselves are confirmed. So the events are solid; the minor gap is only in how firmly the numbers can be pinned this run.

By July 22, 1969, a Tuesday, the day had thinned to a single midweek bill at the Family Dog on the Great Highway: Congress of Wonders, a comedy act, paired with the Cleanliness and Godliness Skiffle Band. It carries low poster-art weight and its poster number is an honest gap, so it's noted for completeness rather than dwelt on.

The other three years are nulls, and two of them are worth a line to explain why. July 22, 1965 predates the scene. July 22, 1967 was a Saturday, but the Yardbirds - sometimes loosely associated with a Fillmore date around then - were actually in Santa Monica that night; their Fillmore run didn't come until July 25-30, so there's no core SF ballroom event to log here. And July 22, 1968 was a Monday with Fillmore West dark; Sly and the Family Stone played the Circle Star Theater in San Carlos that night, which is nearby but not the ballroom scene. All three, then, are honest nulls at the core venues.