In this question someone asked how updated items with new affixes worked, and I answered that items with altered affixes are generally distinct, new items, and that existing items are no retroactively updated.
Here's an interesting scenario that may have come up previously because of this but which will almost certainly come up a lot with 2.4.0. Say I have an existing 6-piece set. Then the patch drops, leaving those existing set items intact, but I then go and find 3 pieces of the updated set. What bonuses do I have?
My guess is that I would have the 2-piece bonus from both the old set and the new set concurrently (or, if I have a RORG equipped, the 2-piece and 4-piece bonuses concurrently).
Does anyone have experience from any previous set updates or the 2.4.0 PTR that validates (or falsifies) this hypothesis? For bonus points, are there any circumstances in which you've found this advantageous (eg. double-dipping on similar or identical set bonuses)?
I understand that I'm probably inviting a lot of speculation here; I'm specifically looking for people with existing experience of this situation to comment on it.
Best Answer
As mentioned in the comments, sets are always updated retroactively, most likely to prevent scenarios like you desribed them.
Here is a blue post describing the situation for the patch 2.2
Since it has been the same for patch 2.3 and 2.4 on the PTR (there were even several changes while the 2.4 patch was on the PTR and those changes were also always retroactively) it will most likely be the same for future patches.