On Thursday, September 12, 1968, Bill Graham's BG-136 opened at Fillmore West, and the bill reads now like an accidental group portrait of a scene at its hinge: Big Brother and the Holding Company headlining, Santana beneath them, and Chicago Transit Authority at the bottom — three futures diverging on one Rick Griffin poster, September 12–14, with lights by Holy See (bill, dates, and credits per wolfgangs, famsf, and rockposters). Griffin's sheet is the kind of dense, liquid lettering the poster catalog prizes, but the names underneath are the story. This is late-Joplin-era Big Brother: Janis Joplin's final show fronting the band would come on December 1, 1968, so on this Thursday she was still theirs — the split already rumored, the departure not yet fact. Below her sat an early-rise Santana, a house-favorite Fillmore act still months from Woodstock and the first album, riding the residency circuit that Graham used to build his locals into headliners. And at the foot of the poster, Chicago Transit Authority — the full name, spelled out, because they had not yet become simply "Chicago"; that shortening came in 1969, after the real transit authority reportedly leaned on them (the abbreviation-and-legal-pressure account is the widely repeated one, so take the specifics as lore rather than documented fact). Three tiers, three trajectories: a headliner about to lose her band, an opener about to break wide, and a bottom-bill horn outfit about to lose a word from its name.

By the next September the room had turned over its cast entirely. On Friday, September 12, 1969, Fillmore West was mid-run on BG-191 — Steve Miller Band over the James Cotton Blues Band and Keef Hartley, the Randy Tuten poster carrying a September 11–14 stand whose anchor night was the Thursday opener (bill and dates per wolfgangs and rockposters). The 12th was night two, a continuation rather than a premiere, and worth noting mostly for how routine it had become: Steve Miller headlining Graham's flagship was, by 1969, unremarkable in the best sense. Which is its own small joke on the calendar, because two years earlier Miller had been playing the September 12th slot in a very different room.

Back on September 12, 1967, it was the Steve Miller Blues Band — still carrying "Blues" in the name — settling into a September 12–14 run at The Matrix, the small Fillmore-district club, with Peter Walker opening and the lighting billed, with a wink, as "Lights by Gum" (per coau and rockprosopography101). No poster; the Matrix worked as a residency room, so the record here is club color and the date-page ledger rather than a printed sheet. Still, the throughline is hard to miss: the same bandleader, the same week of the month, climbing from a club billing to the top of Graham's marquee inside twenty-four months.

The stranger September 12 entry belongs to 1969 as well, out at the Family Dog on the Great Highway, where It's A Beautiful Day headlined over The Fourth Way for a September 12–14 stand, wrapped in the Garden of Delights (per rockarchaeology101). A word of caution on that last name, because it's the kind of thing a careless index turns into a fourth band: the Garden of Delights was the light show, not a group on the bill. Sons of Champlin may also have played this run, but the placement is disputed, so leave it as a maybe rather than a fact. And there is no printed poster to hang any of this on — the FD-6909xx code that floats around for this date is a date-stamp placeholder, not a real Family Dog catalog number, so anyone citing it as a poster is citing a filing convention, not an artifact.

(1967: the Steve Miller Blues Band at the Matrix, three years and one dropped word from the Fillmore West headline. 1966: nothing distinct on the SF-scene ledger for the 12th — at most club color from the Matrix's Blues Project residency. 1965: no dated poster event, the ballroom scene barely underway.)