I have a follow-up question:
If you do an in-plan conversion from pre-tax or after-tax 401k to Roth 401k, then after the conversion, which portion would be treated as basis in Roth 401k?
Let's say you originally have 1k after-tax contribution, 0.7k earnings from after-tax contributions, 2k pre-tax contributions, 1.4k earnings from pre-tax contribution. And you roll-over everything into a empty Roth 401k.
Then, the resulting Roth 401k has how much basis and how much earnings? The number is importance when you do an early withdrawal from Roth 401k.
