My parent died 12 years ago, and I just discovered they had 300 hundred shares of stock held by a third-party stock transfer agent.  The stock has paid some dividends but the amount in total would be less than $1,000 over the entire period. How do I record this payment? Would I record it the year I received it, or would I be required to refile 12 years of returns? It is my assumption based on what I found that income tax was withheld by the company in my parent's name but yet to confirm that.

I assume the stock basis would be at the time of death based on step up. The original basis for my parents would have been much higher than the value at death.