That's just bad management of airdrop. If you joined a previous phase (like the first one in my case), you can't join again because you would need a different email address I guess, since when I access the link it says that I already responded to the form and even if I edit it, it does not add my address at the back of the queue.
Like I said, this is not good and you should find another method if you stated that those who applied for airdrop in previous phases can join again, when IN FACT, we CAN'T!