How to handle reissued tokens

[Goldmund]

I had this issued resolved in another thread here:

Token upgrade new contract address

Hi, one of the token I has is upgrading to new contract (let say from TOKEN to TOKENv2), meaning, the old token will be worthless soon, and I will have the exact amount of TOKENv2 as it was in TOKEN. The old contract itself won’t be removed from the blockchain, its permanent in blockchain. How do I handle this situation for tax?