Hello,
If you are able to get this data sheet and if they are standard in your company you could use IDM rules. If this is mostly excel sheet defined by each users, you could use keywords based on headers. If these data sheets always contains some identifier well formatted you could use regular expression (or a custom data identifer created by yourself if there is many different format).
Defining a DLP policies on unstructured data is always a mix between finding common criteria on all document/data/information you wanna protect and the fact that you must not generate more incident that you will be able to assess.
Regards