User blog comment:Omega natsu2/Chapter 369: The Place Prayers Reach, Predictions./@comment-7418318-20140124102319

Fairy Tail:
 * Jellal somehow managed to put the seal within him into a thought projection and that is what was "killed".

To explain: While it's possible that the turned up at the council in person, it's more likely that he "got" the seal onto his Siegrain thought projection. And if the Demons are correct, he'd have absorbed it along with the magic, when he rejoined at the Tower of Heaven. If it was possible to put the seal on the thought projection and absorb it, maybe the reverse is also possible.

I wouldn't be surprised if he tried to "free" OS by making them believe they had killed him, for which a thought projection would be a very good choice. It might also explain why Cobra isn't simply dodging all of his attacks, since he may not be able to hear the thoughts of a projection.

If he just "reactivated" old Siegrain, he didn't even need to be aware of being a "sealer" to pass the seal over to Siegrain.

And the reason why Crawford took so long to find Jellal's signature might be because the real Jellal has concealed himself and Siegrain has a slightly different signature.