The Fifth Old God Controversy: Examining the Titans' Claims

wowhead.com:

In Patch 7.0.2, an annotated version of an old lore book reminds us about a fifth Old God — a being who has been present in every version of this in-game book, including a version that was added to the game around the same time that Chronicles Volume II came out — and yet is strangely absent from the Chronicles series. We've already reported on The Old Gods and the Ordering of Azeroth (Annotated), a new updated version of the Classic book, The Old Gods and the Ordering of Azeroth. The original book is about early Titan lore, explaining how they came to discover Azeroth, only to realize it had been infected by the Old Gods. It briefly describes the Old God control of Azeroth, how the Elemental Lords ruled their armies, and how the Titans eventually gained victory and chained the Old Gods beneath the earth. It goes on to detail how the Titans empowered certain races, created the earthen, and established the Well of Eternity, before finally naming the continent of Kalimdor. While the new version is almost exactly the same, it also includes scornful notes on every page — written by someone who does not like the Titans at all. The most interesting thing about this book, however, is the mention of a fifth old god.

Chronicles Volume I only mentioned four Old Gods: Y'Shaarj, who they killed and whose death caused so much damage to Azeroth they decided never to risk killing another Old God again, N'Zoth, C'Thun, and Yogg-Saron. There is no mention of a fifth Old God being encountered or imprisoned, making it easy to assume any lore about a fifth Old God was retconned by the time the first volume of Chronicles came