The Adventurer's Companion includes a host of new rules too, from new combat options and a new calling, the Captain, to rules for generational play and expanded rules for holdings.
Scoured my copy of AC - nope, nothing about holdings.

So I may have missed earlier explanations or discussions on this but what happened?

I did find zed's Events for Holdings thread from 2014 viewtopic.php?f=7&t=1720&hilit=Expanded ... r+holdings - very interesting....