No, I would not put it in Screen 24 until it's rolled over to a Roth IRA. When the taxpayer rolls it over, the custodian should give them a report of the basis that the taxpayer should give to you.
If you don't get that, I would push the client to request/find it, warning them of their homework (or your bill) to go back through all their W-2s every year if they don't get it.
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