The technical answer is the year the stock became worthless, but that can be hard to determine. Date of dissolution has no bearing so scratch that one. If you read court cases the IRS will disagree with taxpayer as to the correct year, sometimes they say too early, sometimes they say too late. If they say it occurred in a prior year, and the statute has closed, deduction lost. But If assets were distributed in a year, that sounds like a capital loss on a sale, since proceeds were received, is that correct ? Worthless stock means no proceeds of any kind.