How many limited-time quest-rewards have already passed?

[Enkidoh]

Well, there's been at least three seperate seasonal events which have come and gone since launch - a very late Summer event (Moonfire Faire), which had new and old 1.0 swimwear, the Halloween event (All Saints Eve) which had ghost costumes and Halloween inspired food items along with the Pumpkin head costume headgear from 1.0, and finally, most recently, the Christmas event (the Starlight Celebration) which had snowman costumes and Santa sleigh barding for your chocobo plus the Santa and reindeer costumes from 1.0. All these events are classed as 'seasonal', so they should all return (with new items plus the old ones for sale) when the time comes.

The only other special event that happened was the FFXIII Lightning event which gave players Lightning and Snow costumes plus FFXIII/XIII-2 themed weapons, but that should be returning in February to coincide with the international release of Lightning Returns. So you'll have a chance to do that.

Other than these events, the only other 'bonus items'/rewards that were formerly offered but are now unavailable are mostly related to version 1.0, specifically the Legacy Campaign (special chocobo mount, name in credits), or items and achievements that were only offered in 1.0 and are now unattainable, like the Hermes Shoes and the Gobbuue Mount. SE have stated these will never be available again, so sadly if you didn't have 1.0 and gained them then, you're out of luck I'm sorry to say.

[Niwashi]

Well, there's been at least three seperate seasonal events which have come and gone since launch -

Plus a fourth that's come and not yet gone. The Heavensturn (New Year's) event lasts until Jan 14th I believe. (Its quests start in Gridania, then have you travel to Limsa Lominsa and Ul'dah, so you'll need airship access unlocked. The quests are kind of silly and reward the horsehead helmets used during them. But you can also simply buy the helmets that were created for previous years' Heavensturn events. I like the ones from the year of the dragon.)

The Lightning Strikes event has IMHO the best rewards of any of the events so far, but to get all of them you need to be level 45, although you can get all the weapons by level 15. (Earlier for characters who start in Limsa Lominsa, who can do so by around level 9 or 10. The 15 requirement for others is because they have to be able to get to Limsa Lominsa.) I'm a little disappointed. With my only female alt being currently level 13, there's virtually no chance I'll be able to get Lightning's coat when the event comes around again (as I'm pretty sure that one's the level 45 reward). Snow's outfit isn't nearly as cool looking.