Isn't that the document (cheque) number? All transactions have one of those.

All transactions also share a description field. You can also use the optional fields too.

All Adagio modules with a document designer have a specification available that will print all the fields you can use and their contents. In Receivables V9.0A this is called "All codes: Matching". Print out a statement using that form to see what's available to include on the form.

What are your customers finding confusing about your statement?