They're added to the drop pool as soon as the event goes live, what I'm saying is that during a drop rate increase you can still get the new item with unclaimed packs, just that you'll have the same chance of getting it as any other LM
(Not really a loophole, it's the same result as buying packs after the drop rate event ends)
Pretty straightforward, the number of items in all your unclaimed boxes = the limit i.e. you can store more mix boxes than 5x silvers, it doesn't vary between accounts
(1,000-1,500 mix boxes vs 200 5x silvers)