The rules
Agree the daily set before day one, write it in the challenge description and keep it fixed for all 75 days.
Tick "All daily tasks done" only when every task is complete. Partial days do not count.
The leaderboard counts completed days inside the dates. The app does not reset anyone after a miss; if your group wants a strict "start again" rule, agree it between yourselves.
Most completed days wins. Ties share a place.