Maybe this could help:
FAQ: Upgrading SEP 11.x to 12.x
http://www.symantec.com/docs/TECH207274
With SEP 11.x, you can continue using it, but you are not entitled to support, updates and upgrades after its expiry date on its paper license (the yellow paper).
"If lets say we renew SEP license, should we get the latest SEP version CD?"
Either you can have its DVD (no more CDs), or you can download the whole thing from the Symantec Fileconnect website. Do this after you have read and understood the FAQ mentioned earlier.
Hope that helps.