Roth IRA contribution withdrawal

[Section108]

My wife's Roth IRA was transferred from TD Ameritrade to Schwab in an acquisition a couple of years ago.  While we personally may have statements going back to show what her contributions were in 2006 and some subsequent years (in any case we do know the exact amounts), Schwab appears to have no records nor knowledge of them, and only has online statements for the most recent 10 years; so if she were to withdraw her contributions, which she's allowed without penalty or taxation despite being younger than 59 1/2, indications are that Schwab will default to reporting this as an early withdrawal (their online transfer page we're looking at calls the pending amount we entered pre-tax, with no option to correct).

My concern is, when doing the tax prep next year, having made the withdrawal, will Turbo Tax allow me to correct any incorrect info it captures from Schwab tax documents I upload?  All my research so far at IRS and others point to filing a Form 8606.  There's no mention of how to prove the contribution amounts, even assuming I can locate the old statements from the relevant years.

Thanks

[Opus 17]

The broker would code the distribution as "early distribution, no known exception."  Turbotax will ask if any exceptions apply, and you be able to enter the amount of your prior contributions and any other prior withdrawals.  If your contributions are larger than your withdrawals, the withdrawal will not be taxed.  You don't attach any documents or proof to your tax return.  Your signature of your tax return is your self-certification that your figures are true and accurate.  If the IRS decides to audit you (less than 1% are audited), then it is up to you to show by records and other information that your figures are accurate.