Read my Thread, it will be only for 50s the epic box for the mount, next expansion 60. Blizzard confirmed their awful idea to move the limit each expansion.
This should be removed, actually it’ll be better if we can spam it with a single characters, there’s players that say this could remove rarity from the mount, but that mount is the worst drop at 0.03%.
Also you can do a counter argument that if a player already have the mount, it could be less or more rare depends on the patch on which that player obtained it, because some patches the boss was farmeable by the same character without an ID and then it was farmeable by characters level 14+ and now we’ve the worst barrier to farm it.