Adobe Sign API Agreement Documents - Is there a way to specify/track an External ID

We are developing an Adobe Sign integration, where documents are sent for signing from a third party systsem - Is there a way to track the documents external ID (The Agreement API end point allows for us to send an externalID parameter). Currently we are using the transient document end point to upload the document then using this transient doc id to add the doc to the agreement - however when we query the agreement later in the process the documents get new IDs and we are not able to track which document links back to the third party document we initially uploaded.