User blog comment:Omega natsu2/Chapter 369: The Place Prayers Reach, Predictions./@comment-4449950-20140128032255/@comment-7418318-20140128094857

Regarding the real names: With so many slaves and them being held in different cells it's possible that they never met prior to the revolt, so that might explain how Erza and Cobra didn't recognize each other.

But Jellal stayed on the island after Erza was forced to leave and after the slaves were set "free". So Jellal had more opportunities to meet them.

On top of that Jellal was probably the one to select which of the children would be given over to Brain, or he accompanied Brain while he selected the candidates.

Or Brain might have mentioned their names when he taught Jellal new spells.

There are enough possibilities for Jellal to learn their real names that I won't get suspicious about it.

A little note: While Cobra, Angel and Racer were shown surprised, Hoteye wasn't shown at all when Zero woke up. Maybe it's just an oversight or a lack of available frames. Or maybe it means that Hoteye is in on the reason why Midnight smiled.