If you sold the first one for 70, the one you get later might sell for 80, but this is not certain.

The key question is, does y also lose 15 points? If x sells the airdrop for a value of 100u, and by the time it's y's turn, it's only worth 50u, then losing 15 points doesn't make sense, unless y doesn't lose points or only loses 5 points, which would be fair.