On Thursday, September 14, 1967, Bill Graham's BG-83 opened its three-night stand at the Fillmore Auditorium — Jim Blashfield's mating-birds design fronting the Electric Flag, Mother Earth, and the LDM Spiritual Band, Thursday through Saturday, September 14–16 (poster inscription "Thurs/Fri/Sat — Sept 14 15 16," per the V&A record, accession O107084, which also carries a bonus "A Grove of Indian Musicians" line; bill and dates cross-checked against wolfgangs and rockposters). What makes the night worth stopping on is who was headlining: this was Mike Bloomfield's Electric Flag, the band he'd assembled that spring after walking away from the Paul Butterfield Blues Band, a horn-driven "American music" outfit that had made its formal debut only three months earlier at the Monterey Pop Festival in June. By mid-September the Flag was no longer a rumor built on Bloomfield's reputation — it was a working band being booked into the Fillmore on its own name, a squarely post-Monterey moment for one of the scene's most-watched guitarists. (Worth keeping separate in the catalogue: the Flag had already played the Fillmore that summer, sharing an August 8–13, 1967 bill with Moby Grape — a different stand, a different poster, a month earlier.)

The Matrix, meanwhile, was closing out its own residency that same night. The Steve Miller Blues Band, with Peter Walker, finished a September 12–14 run at the little Fillmore Street club — no poster, just the club's rolling calendar (per coau). It's a small thing, but it rhymes with the room's origins: the Matrix had opened barely a year earlier, on August 13, 1965, with Jefferson Airplane installed as the house band (Matrix history per wikipedia). And exactly two years before Steve Miller's closing night, the room was still in those first weeks — on Tuesday, September 14, 1965, the bill was Billy Roberts, the man who wrote "Hey Joe," alongside Jean Ball (per coau, with the club context from wikipedia). Roberts playing a Tuesday-night set in a folk club that had opened a month prior is about as ground-floor as the San Francisco scene gets; a year later the ballrooms would swallow that intimacy whole.

The following September the date belonged to the bigger rooms. On September 14, 1968 — a Saturday — two three-night runs were both hitting their final night across town. At Fillmore West, Rick Griffin's BG-136 closed out a September 12–14 stand with Big Brother and the Holding Company, Santana, and the Chicago Transit Authority. At the Avalon, the Wes Wilson–Kurt Strausse poster FD-137 was in the middle of its September 13–15 run, night two of John Mayall, Big Mama Thornton's Hound Dog Band, and Black Pearl (both bills per wolfgangs and rockposters). That the Chicago Transit Authority and Santana were on a Fillmore poster at all is a marker of how fast the roster was turning over in that stretch — bands that would define the next couple of years still billed under and around the Monterey-era veterans.

There's one more 1968 item that belongs in a footnote rather than the body. Jack O'Connell's documentary "Revolution" — the 1968 San Francisco scene film that put Country Joe and the Fish, Quicksilver, and Steve Miller on screen — did get screenings around the city, and one lineage places a Straight Theater showing on September 14, 1968, paired with Congress of Wonders. But that specific date rests on a single community-wiki thread and can't be corroborated; the film is real, the September 14 screening date is unverified and held for review.

By the next year the date had settled onto a closing night again. On Sunday, September 14, 1969, Randy Tuten's BG-191 wrapped a September 11–14 run at Fillmore West with the Steve Miller Band — the same Steve Miller who'd been closing out Matrix residencies two years earlier, now headlining the big room — backed by James Cotton and Keef Hartley (per wolfgangs and rockposters). It's a tidy arc for a single calendar square: the blues-club sideman of 1967 headlining the Fillmore by 1969, with the horns of the Electric Flag and the ballroom double-bills filling in the years between.

(1968: BG-136 closing at Fillmore West and FD-137 mid-run at the Avalon, with the "Revolution" screening unconfirmed. 1969: BG-191 closing at Fillmore West. 1965: the Matrix barely a month old, Billy Roberts on a Tuesday. And earlier — 1966: no catalogued San Francisco ballroom bill anchors this particular date.)