Bring the pieces back together. One person names the memory, the people who were there each add a line, a photo or a recording, and the story writes itself from what everyone remembers.
Just enough to jog everyone else. You can change nothing later except by adding more.
Name the event, the date, the place. Ask one question.
A private link, or a code to scan, for the people who were there. Nobody else.
Every contribution, in the group's own words, becomes one story with every line attributed. Disagreements stay in.