you just need same 3 keys in client and server. except you want extreme thing, in server u decide "hey I want theses keys for 2011 client, these keys for 2012 client, and these keys for 2013 client" IN SAME TIME
because u're talking about multi-client support, I want connect to use 2011 from PC A, use 2012 client from PC B to server X, so server X store alllllllllllllllllllllllll keys for alllllllllllllllllllllllll client dates, what a ...
nah, multi-client doesn't have issue for me, except each client send static-and-cannot-be-changed-keys and each client send different encryption methods.
The fact, (at least 2012-04-10a & 2013-08-07) clients send same encryption method, and I tested with 2 different client with same keys.