The first entry is always the pin's source. Overall confidence is a weighted average of how firmly each reference supports the start and end times used above; a reference counts half as much for every 180 days older than the newest.
Happened as dated, per macrumors.com: "…most significant in years thanks to the debut of a radically redesigned iPhone that features an edge…"
AppleInsider (31 August 2017) confirms Apple "invites press to Sept. 12 event at Apple Park's Steve Jobs Theater," matching the pin's stored 12 September 2017 date and 'Let's Meet at Our Place' framing.
MacObserver similarly confirms Apple sent media invites for a "September 12th 'Let's meet at our place'" event at the newly opened Apple Park venue, corroborating the pin's date and title.
Something missing or wrong? Say it in your own words: a link that backs this pin up, a different start or end date and why, or a fact it lacks or gets wrong. The AI checks it against this pin's sources, searches for better ones, and adds any page that backs you up. The pin's own sources still count most.