Once you hit age 59-1/2 (and your Roth IRA is more than 5 yers old), there is no need to track the source of your Roth IRA funds as coming from contributions, conversions or earnings. All withdrawals from a Roth IRA are tax-free regardless of the source of the money.
(If you do want to keep track, you do that yourself, it is not part of any tax form and does not get reported to the IRS. For someone under age 59-1/2, if they claim a withdrawal is tax-free because it is contributions, it is up to the taxpayer to prove it from their records if audited.)
