I have installed the 2015 connector on the server and installed 2015 application on a workstation and am currently converting the data from 2012 to 2015.  I will repeat the process with 2021 on the server and workstation.  Once this is complete, is it necessary to upgrade the application on the remaining workstation from 2012 to 2015 to 2021 or can I just go directly to 2021 application on the workstations?