Hello @Carlton_Hoy, welcome to the Asana Community Forum!
Metadata fields might be very helpful in this case as one field is “completed on”
Have a look here: Tasks Metadata now appear as Custom Fields within your Project or Users in custom fields (Created by) - #26
Hello there,
Is there a reason to not allow completed date to be editable? With the amount of requests asking for it, it just seems like a simple feature to implement.
Relying on a custom field just seems like a workaround to me, as that would now just be an additional field that needs to be maintained. Unless the “Completed on” meta field is updated when the checkmark is checked, but I don’t see those toggle-able meta fields in the UI, only the ability to add a custom field.
Thanks!
Welcome to the Asana Community Forum @Christopher_Peterson 
“Is there a reason to not allow completed date to be editable?”
Yes Asana has implemented these fields to have some specific data that is pulled based on real actions. It would not really make sense if people then amend the data so it is not actually based on when something happened.
“Unless the “Completed on” meta field is updated when the checkmark is checked”
Whenever you mark a task complete it will show the relevant completion date in this metadata field
“don’t see those toggle-able meta fields in the UI”
In list view go to “Hide” from where you can select which fields to show and which not.
Thank you, I just realized that you responded to this.