We've got another update coming in for the expected tweaks for World of Warcraft's game patch 2.3.0, with this latest matter pertaining to the MMORPG's arena gear. As Kalgan explained over at the WoW forums, Arena season 1, 2, and 3 armor sets will now be part of the same set. Quoting the Blizzard spokersperson's full explanation:

As of patch 2.3 all items in the gladiator season 1, 2, and 3 sets will be part of the same set, so you can use those items interchangeably and keep the set bonuses (ie: you can wear the season 2 shoulders along with the season 3 helm, chest, legs) and retain the 4 piece set bonus.