When I check the list of items in League of Legends under "Item Sets", and search "Doran's", I get two versions of each of the Doran's items (Doran's Blade, Doran's Ring and Doran's Shield), the normal and the "Showdown" version.
What is the difference between these two versions of items?
2 Answers
One is for showdown the other is for the base game. Snowdown Showdown is a seasonal game that features re-balanced items, such as doran's ring. In showdown, you can only have 2 doran items. The showdown ring remains the same except that the mana regen is no longer a passive. The showdown shield gives more health and regen and the regen is no longer a passive. The showdown blade is identical except for the cap on doran items.
In addition to Jake's answer, if you actually make the item set and aren't in the place you have the set for, it won't show up. Tear of the Goddess (http://gameinfo.na.leagueoflegends.com/en/game-info/items/) for example has a Crystal Scar and "normal" version. If you just put "normal" and play Crystal scar the Item Set will show but the Tear will not. General rule there but applies to the Q.