I interpret your question to mean the middle name on the signer's license is Steve, but it's Stephen on the documents to be signed. It's common to accept short forms of names to be equivalent to to the longer version, if all the other information lines up. You could decide to accept it if you're reasonably certain the signer is the person being described in the documents.
In my acknowledgements, I always write exactly what is contained in the document. It's my job to decide if the person in front of me is the person named in the document. The ID card is just a means to that end.