It will mostly depend on your own implementation (how you wrote your remote functions, for example) if your Server will be able to handle parameters received from old and from new Clients.
As far as the RTC SDK goes, it is safe to use Clients compiled with an older RTC SDK version (or even different older RTC SDK versions) together with a Server compiled with a newer RTC SDK version. What you should NOT do, however, is use a Server compiled with an OLDER RTC SDK version together with a Client compiled with a NEWER RTC SDK version.
In other words, if you keep your own Server-side code backwards compatible with your older Clients and you always upgrade your Server(s) before upgrading any of your Clients, you will be on the safe side.
It would be a good idea if you would have your Clients auto-update themselves (download the latest version from the Server) every time they are started, so your Clients do not continue using the oldest versions for too long, so you do not have to keep your Server code compatible with very old Clients, but ... there should be NO breaking changes in the RTC SDK which would force you to upgrade your Clients every time you upgrade the Server. The whole idea of the RTC SDK is to allow you to use Clients of different versions with the same (new) Server, and NOT to force you to upgrade all Clients every time you upgrade your Server.
Best Regards,
Danijel Tkalcec
Thanks for that Daniel - really good information to have, and a really nice feature of the sdk.