Automatic Checkbox w cross-sheet & lookup

Paul Newcome

=IF(ISDATE(INDEX(COLLECT({19-20 Sign In: Rehearsal Date}, {19-20 Sign In: Dropdown}, $[Dropdown Name]81, {19-20 Sign In: Rehearsal Date}, DATE([September 11]$90, [September 11]$91, [September 11]$92), 1)), 1)

 

There was an extra closing parenthesis. Try this.

 

The above is incorrect. I need to take another look. As long as your ranges are correct, there shouldn't be a problem with the formula. Are the date columns in the other sheet set to a date type, or is it a text/number type?