It's also relatively easy to enforce with a generic assertion that all inherited assets must provide proof of adequate payment of capital gains taxes or carry a

It's also relatively easy to enforce with a generic assertion that all inherited assets must provide proof of adequate payment of capital gains taxes or carry a cost basis equal to the earliest point from which proof can be established. I'm sure there would be hijinks to avoid this, but for the amounts in question a great deal of legal and accounting hours could be expended to audit the correctness of the returns.