Looking at the flights of one club last year (for example), he
https://www.onlinecontest.org/olc-3....S&sc=1&sp=2017
the dates are off by one day. E.g., the flights listed on August 25 really happened on August 26, as can be seen by looking at the detail info page for a flight, or by clicking on the OLC 2.0 layout button.