The police are still able to retrieve data despite the factory reset on Jung Joon Young's phone. 

At the press conference on March 25, commissioner Min Gap Ryong stated, "He did take action on his phone but we've obtained other data. We believe it will still be possible to check the original content (of the phone) by comparing the data."

Back on the 22nd, Jung Joon Young revealed to have factory reset one of the three phones submitted to the police. The police initially attempted but failed in reviving the data.