I created a mail merge from a query and I see that some constituents have a blank opt-out field even though Accept Email is No. Why are some opt-out dates blank while others are populated?
If you did that Mail Merge from Query results, then it's possible that you are including constituents who have been removed. If the constituent opted out a long time ago and is removed, than we don't keep that information. Add the below clause to your Query:
Field Type: System Field: System Active Status Is not equal to Removed