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.
Estimated: the 17 September 2020 practical completion Buildington[3] records is for the neighbouring Grade II* listed 20 Hanover Square, not 18 Hanover Square. GPE's[2] release of 12 May 2021 says the final office letting came 'less than six months after practical completion', putting 18 Hanover Square's completion after mid-November 2020, so the pin takes the end of that quarter. No source gives the day.
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