Are you certain the value of the stock was not included in a tax reporting statement when you received it?
Yes, I was a top 10 earner and it was given to me by my small company at the time. My boss said hang on to it, it may be worth something someday, none of my papers provide any value. That was 15 years ago and the stock went public 2 years ago and I sold it this year. I am trying to determine how I come up with my cost. when the stock went public it was worth $17 per share.
The basis of the stock would be what you paid for it or the value that you included in your tax return income in the year that you took possession of it. If you didn't report the value on your tax return in the year that you received it 15 years ago, and you didn't pay anything for it, then you need to compensate for that by listing the cost basis as $0 in 2023, the year that you sold it.