To know what items are in what world and are owned by which player you can take a look at Tibia: Rare Items When you look at the world list on Tibia's website and you hover over the BattlEye symbols it will remind you what it means. Also, to know when a world is created click on the world on the world list and look where it says creation date. If your interested in a summarized list of worlds, BattlEye type, creation and all you can visit Tibia Wiki: BattlEye
green symbolizes the world has been protected by BattlEye since the creation of the world
yellow symbolizes the world has been protected with BattlEye since a certain date after the world's creation.
Please note, the list can be easily outdated and might not include all worlds. I will give you some information currently on the list that is in green BattlEye worlds:
As you can see, these items were won by the Tournament and are considered not obtainable. The reason why there are not many "unobtainable items" in green worlds is that on April 18, 2017, is when the first green worlds were created: Vita, Noctera, Honbra... and many followed. Also, characters can only move to a game world that has been initially protected by BattlEye if they also come from a game world that has been protected by BattlEye right from the start. So this is why there are not many unobtainables on green BattlEye worlds due to world transfer restrictions. (Source)
Many of the unobtainable items in Tibia come from very early on in the game unless they are contest/fansite prizes, items that recently became deprecated like Cockroach Legs or Chayenne's Magical Key, items that were bugged like how players brought The Chiller from Dawnport to Mainland for example, etc. What items are no longer obtainable in-game?