You are supposed to keep a record of your Roth IRA basis, that is the amount you have contributed over the years. It may not make a difference if you don't take out money early.
When accurate records are important is when you take money out prior to turning 59-1/2. If your account has been open at least five years, you can take money out early, up to the amount you have contributed, and it is not taxed and not subject to penalty. You need to document the amount you have contributed in order to avoid the tax and penalty.
If you are over 59-1/2, or if you don't ever take money out early, don't worry about the Roth basis questions.
If you may need to report your Roth basis at some point, you should enter the amount that you can document now and keep an annual record of contributions.