Historical clue formulations

• Christopher Street Day celebration — 2022-01-02
• Big outdoor June event — 2022-01-01
• N.Y.C. event on the last Sunday in June — 2020-09-25
• Outmarch? — 2018-05-18
• Annual June celebration — 2018-01-13
• *Event with rainbow flags — 2016-03-20