You actually only lost out on $4k worth of BitCoin. As you stated yourself, a few months later when you remembered that you threw the drive away with the curren

You actually only lost out on $4k worth of BitCoin. As you stated yourself, a few months later when you remembered that you threw the drive away with the current value at $4k, you said you could have used the money then. It's safe to assume that if you still had the bitcoin then, you would have attempted to sell at that price. Also, regarding the proof of ownership for the drive, if found, do you still have the receipt or conversation about purchasing the bitcoin in the first place? Tax wise, you should always keep that when purchasing collectibles to have proof of your cost basis, in the U.S. at least. Not sure about other countries regarding capital gains like taxes. But if you had proof of purchase, I'd say that would hold up strong if the drive was found, at least for the value derived that text file. Your account holding the value is not in your harddrive, it is on the bitcoin blockchain, you just lost your key to get the bitcoins stored in it. But at the same time, once you throw something away, it is assumed you have given up all rights to it, thus the person who finds it now has all rights to any information on the drive, including your private key.