The initial transition from Vanilla -> TBC was dealt with in the way that they updated the "Classic" client to TBC and then added "Classic Era" as WOW TBC Gold an option for download. All characters were transferred to "Classic Era" as well as both "current" and "Classic Era" versions were disabled. The next step was to choose which version you wanted to activate. This would stop you from using the other copy (the majority of the characters were activated with only the TBC version).
Thinking about the name "Warcraft" We haven't seen that much in the vanilla version and TBC. Plain wars between alliances and hordes, aside cheap Burning Crusade Classic Gold from battlegrounds, there's any action.