It would make no sense to send a code five months prior to release, and it would make no sense to send CEs five months prior to game release. Simple as that, and the delay is no doubt the sole reason.But the collectors edition at least for the PC does not contain the game - it only contains a download code (and other stuff). There is no reason why the code couldn't be given in advance, as download becomes available only when the game actually launches.
Also, I'm not sure what you say is even how it works. Codes associated with a non-existent game sounds unlikely.