I received a 1099 on a stock sale but one of the sales does not have a date of sale or cost basis. This is because the original broker turned over the stock to the state of MA and when I retrieved the stock this information was stripped off. I have the original basis values on a spreadsheet but the original broker and my former employer [it was stock purchase plan] say the no longer have that data. Can I use the dates and basis values I have on my spreadsheet and what happens when they don't match the data passed to the irs from my broker?