74 (oldest version found, you can only kill mobs, level and some other small stuff)
97 (base version, normal and excitems, wings level1 and 2, level2 quest, devil square, blood castle, max items +11)
99 (darklord, chaos castle, max items +13)
season1 (crywolf, castle siege, ancient items, malron spells,quest)
season2 (SD, Kanturu, 380 items, harmony options, other items)
season3episode1 (Level3 wings, Level3 quests, illusion temple, silent map)
season3episode2 (SkillTree, New Interface, summoner, items)
Season4.5 (quest system, socket items, raklion, moss merchant, map, vulcanus, items)
Season4.6 (duel system, other)
Season5 (new events, summoner skilltree, +15 items, items, maps, gens)
Season6 (new ancients, ragefighter, ragefighter skilltree, maps, improved cashshop and more interface options, autobot, maps)
ex700 (element system, PVP event, item, maps, skilltree update, level cap increased (ML probably), other)
This is 95% accurate, I hope this helps