In terms of the 'max', ethereal rare or Unique items upgraded using the Horadric Cube are set to the maximum Durability of the base Exceptional or Elite item. For example, when ethereal Shaftstop Mesh Armor (Durability [45/2] + 1 or 23) is upgraded to Boneweave, it now has maximum Durability 45.
There is an example of it in this thread:
http://forums.d2jsp.org/topic.php?t=73212484&f=103&p=494400264Quote (guttermouth @ Mar 17 2018 09:44am)
is there any way to assure fuller durability after an upgrade?
No, ethereal items always spawn with full durability, when you transmute them the remaining durability is randomised. I believe the randomised range may even be from 1 to max, which means you could be extremely unlucky
This post was edited by Marieusz on Mar 17 2018 06:06pm