To clarify—
2012-'13: December 18 [confirmed[/url] (18.3% acceptance)
2013-'14: December 16 [url=https://www.princeton.edu/news/2013/12/16/princeton-offers-early-action-admission-714-students-class-2018]confirmed[/url] (18.5% acceptance)
2014-'15: December 15 [url=https://www.princeton.edu/news/2014/12/15/princeton-offers-early-action-admission-767-students-class-2019]confirmed[/url] (18.3% acceptance)
2015-'16: December 16 [url=https://www.princeton.edu/news/2015/12/16/princeton-offers-early-action-admission-785-students-class-2020]confirmed[/url] (18.3% acceptance)
2016-'17: December 15 [url=https://www.princeton.edu/news/2016/12/15/princeton-offers-early-action-admission-770-students-class-2021]confirmed[/url] (18.3% acceptance) (note: they [url=https://twitter.com/ApplyPrinceton/status/807623461531172864]told them](https://www.princeton.edu/news/2012/12/18/princeton-offers-early-action-admission-697-students-class-2017) when it would be in advance on December 10)
2017-'18: Unknown, but we can probably expect a tweet several days in advance.