So whatever was the story of the missing Deep Dungeon for Shadowbringers?

[dspguy]

ARR didn't have POTD, that was 3.35 with the first 50 floors, and 3.45 released the last 150 floors, so they started in HW.

3.35 patch notes with POTD right up top: here
3.45 patch notes, POTD under the relic step quest under "Quests": here

Right you are. Faulty memory on my part. I was pretty sure I remember running PotD floor 50 shortly before I had to evacuate for a hurricane in 2015. Turns out, it was 2016 - so HW.

Yeah, then the missing deep dungeon for ShB is a bit weird.