If you discover a document that clearly looks fraudulent, or like it does not identify the correct individual, you should talk with the employee about it and ask them to provide alternate documentation from the list of acceptable documents.
On the other hand, if you only find a copy of a document that is hard to read, unclear, or confusing to you, no action may be required to maintain compliance. The US Immigration and Customs Enforcement (ICE) guidance related to internal I-9 audits specifically states that an employer “should recognize that it may not be able to definitively determine the genuineness of Form I-9 documentation based on photocopies of the documentation. An employer should not request documentation from an employee solely because photocopies of documents are unclear.”
There aren't always easy answers for how to handle situations that arise during internal I-9 audits. An employer must balance the risk of being found to have hired and knowingly continued to employ someone without valid work authorization against the potential that their actions will lead to a claim of discriminatory treatment based on immigration status.