One word of advice on the subject of getting everything in FFXII. DON'T.
Seriously. Its ridiculously easy to screw yourself over due to all the arbitrary bullshit the game pulls. The Zodiac Spear may be the most blatant act of easily missable loot but it's not the worst. During the game you'll come across an accessory called the Diamond Armlet that supposedly boosts the value of the treasure in a chest, but after a while it'll start doing the opposite, making it impossible to get the true reward in a chest. This is especially true in regards to rare, one-time only chests found in the penultimate dungeon. And then there's the loot that can be gotten during one-time only fights.
Here is a bit of perspective for the sake of anyone who didn't play it:
- In the Secret area of a dungeon resides the best summon and possibly the best gear in the game.
- The chests containing the best gear can only drop said gear upon their first opening (after that it's random crap)
- The odds of said chest to give you the item you want (and not something like... an elixir) is somewhere around 0.12%
- As Moonson said, the item to increase the odds of good items in chest makes the best items impossible to drop (and the game does not mention this anywhere)
Now, the chests themselves are usually quite far into the dungeon, which is pretty hard (as in can't rush there, gotta travel slowly killing monsters) and there are no save points at all. As such, loading and going back to the chest is about a 10-minute job.
FFXII really missed the mark with the ultimate gear.
Those % would be fine in an MMO if and only if the content could be attempted over and over; not a single-player game with only one attempt.