When sending a signature request (particularly if the document has more than one signatory), you are required to select the individuals to send the request to and then, seperately, select who signs as client 1, client 2 etc.

However, the selection of who signs as client 1, client 2 is not restricted to the individuals the request is being sent to.

I can't personally think of a situation where I would want a different name to appear on the signature block to the person that was signing, so I think the client-1, client 2 choices should be limited to the clients selected for signature request - else this risks the wrong people's details ending up on the signed document.