What would happen if I didn't have the cost basis for a specific year, let's say 2017, but I sold some Undetermined Noncovered Tax lots, and I put $0 as the cost basis. I can determine the cost basis for the funds now and want to sell the funds in the future. Can I correct it by simply using the total of the cost basis for all shares?
Example: Bought 2 shares for $10 each in 2015. Sold 1 $20 share in 2017, reported $0 cost basis. In 2025, I sell 1 share for $40, can I use cost basis of $20 to average out my cost basis across the shares or do I need to stick with my $10 cost basis?
I saw something about a form 3115, but I am not entirely sure if that applies here as it is for an individual not a corporation. TYIA
