"do I have to claim this form? "
Yes. The IRS gets copies of all 1099-B's and will be looking for it on your income tax return.
You'll have to provide the other information - basis and date acquired - if you can. If you can't then use a date sometime around the date you think you acquired the stock and use $0 as the basis. As a Long Term Capital Gain it most likely will be taxed at a very low rate of 0% to 15%.