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?
You can use any reasonable method to determined the stock's cost basis, see more options below. Your broker should be able to share with you whatever they shared with the IRS, so you should not have an issue using your data.