Actually Square has stated that FFXII is the first game Chronologically in Ivalice(I think it's in the FFXII Ultimania Omega) - we also know, from simple logic, that FFXII:RW is next followed by FFTA2(evidenced by the fact that Vaan and Penelo are full-fledged veteran Sky Pirates in FFTA2 and are still little more than pirates-in-training at the beginning of RW)
Vagrant Story is just assumed to be after FFT b/c of the quote by Alazlam Durai at the beginning of the game.

By the way Valendia is the name of the continent that the Archadian Empire is on in FFXII. I would like to know a timeline and see a world map over the ages, because even though the games aren't actually connected, it seems that actions in one game can affect things later in the timeline(you know, like in real history) & I'd like to see how the world goes from FFXII to FFT - where the tech was lost, what happened to all the races, etc.