I realize you probably can't but I just want to verify.
Can I publish a service to 10.3.1 using an earlier version of ArcGIS for Desktop?
Generally, you can use a 10.1 or later version of ArcGIS for Desktop to publish a service to a 10.3.1 server. However, there are some restrictions to publishing if you are attempting to take advantage of functionality exclusive to 10.3.1:
If you're using web-tier authentication for your administrative connection, you must use 10.2 or later to publish.
If you're publishing to a server that is federated with Portal for ArcGIS, you must use 10.2 or later to publish.
If you're publishing a geoprocessing service, the ArcGIS for Desktop version must match ArcGIS for Server.