Hiding Custom Fields

Hi there, we have a bunch of custom fields in the Persons table that have been added over time that we need to clean up and 'hide'. The problem I'm having is you can't hide it if emails/forms have a reference to that field.

The "Filter Used By:" lists all the places that field is in use where it needs to be removed from is my understanding. 

However, in many cases when I go to the email/form that it is referring to, I cannot find a reference to that custom field anywhere. Am I missing something or looking in the wrong place(s)?

Thanks!