There is generally no benefit to keeping separate Roth conversions in separate accounts because all of your Roth IRA accounts are treated as a single Roth IRA for tax purposes. The investment gains subsequent to the Roth conversions or contributions are all simply treated all the same as investment gains no matter which account they are in. The gains are considered in aggregate rather than being in any particular Roth IRA.
Since you are age 73, if your first Roth IRA contribution what for a year before 2017 or your first Roth IRA was established before 2017, your Roth IRAs are qualified and any amount can be distributed tax and penalty free from any of your Roth IRA accounts and there is no need to know basis from gains.
