If I’m ever audited, could the IRS request returns with supporting documentation beyond the three year period?

Generally, the statute of limitations for the IRS to assess taxes on a taxpayer expires three (3) years from the due date of the return or the date on which it was filed, whichever is later. The three-year limit is doubled to six years if the IRS finds that a taxpayer omits from gross income an amount that exceeds 25 percent of the stated gross income. The IRS has no time limit when an audit pertains to assessment of tax if a return is false or fraudulent, reflects a wilful attempt to evade taxation or when no tax return at all is filed.