Interesting that they acknowledge his tenure as a Darklord (which does show up as an Easter egg in Klorr). Though not his brief conquest of Sigil (which was implied to be why 2E's Great Wheel-centered cosmology became the multi-cosmology of 3E), and their default assumption seems to be that he never actually achieved full godhood (which even arguably contradicts the 2014 PHB, where he's "god of secrets").
Includes Icewind Dale spoilers: Perhaps the obelisks were his next step, after trying to conquer Sigil failed. It wasn't enough to rule the present - he had to rule eternity, from the beginning, the First World. Of course, the failure of this effort is what gave us the current canon...