I cannot tell exactly what you've got. So I am going to guess. At least I've seen it happen in this case.
The below only would take place if you're talking about a multiple list of checkboxes. If you have a Value List, with the word "Donors" as one of its values, then you'll only see ones that have values of exactly "Donors" in it. But if you have other values in that field's data, say "Donors " or "Donors Not ", etc., they will NOT show if a checkbox list. But if you do a Find for "Donors," you will also find anything which "donors" in it.
So, you need to view what field in list view without being set to use a Value List, and see what you've got. Likely you can easily change them to "Donors," or something else. If a lot need fixing, a Replace Field Contents could be used. But it's best to save that file as is before running such a script step.
If Fenton's excellent advice doesn't resolve your issue please use Post a New answer to respond back with a more detailed description of your database and what you do to perform a find.
Three other issues that can complicate your find results:
There can be hidden data in your field that is not visible because it does not match one of the values currently defined for the check box value list.
The search criteria might be entered into the field of a related table.
(rare) the file or a field's index could be damaged.