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.
Given as scheduled on the B.A.A.'s Boston Marathon page: "Boston Marathon Apr 19th, 2027 ... 131st BOSTON MARATHON PRESENTED BY BANK OF AMERICA ... 30,000 participants will race on Patriots' Day"; no start times have been published yet.
B.A.A. release: 33,656 qualifier applications for the April 19, 2027 event, from 129 countries, against 33,267 for 2026.[1]
B.A.A. release: the 131st Boston Marathon "to be run on April 19, 2027", registration window 14-18 September and the new random Boston Qualifier Selection of about 1,000 places.[1]
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