There are a few edge cases.
Most nerfs get applied to old items.
There are a few items which mechanic changed like the WD ring RoE.
Set bonis get updated. But if a set item has a new special stat or a buff of these special stat you have to find a new one as well. For example the IK weapon with the stat:
Increases Call of the Ancients Damage by [45 - 60]%