Currently we are unable to add specific order information to individual orders that would then be searchable in Reports. The Reference field is used to add the customer's PO number, so it would be good to have a separate field where we can add additional information.
We are aware there is a Comments field, but this field is not searchable in Reports.
I very much agree with this feature request. I think related to this is having it be a field that can be added as a column to reports and views (such as the All Sale view). The Notes/Comments field could be that field.