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 the source: "the $1bn US embassy in London opened its doors to the public for the first time on 16 January" 2018.
Wikipedia confirms the embassy "has been open to the public since 13 December 2017" and "was formally opened on 16 January 2018," an exact match to the pin's stored date for the formal opening.
Londonist's own piece, "A First Look Inside The New U.S. Embassy In Nine Elms," carries the same 16 January 2018 publish date as the pin's stored date, though the article itself returned a 403 error and could not be retrieved to confirm further detail.
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. A picture that shows something else, or shows it badly, is looked at too, and moved down or replaced.