**Every figure extracted by Claude needs independent verification.** Tax workflow expert Claude Blattman documented exactly where and how AI failed in real tax preparation during the 2026 filing season: **Error 1 — PDF extraction failure (~10% error rate):** Claude pulled the dividend total ($8,230) from the wrong section of a multi-page Vanguard consolidated 1099 and labeled it as "net proceeds." The actual 1099-B proceeds were from a completely different section. Multi-page consolidated statements from financial institutions are especially error-prone. **Error 2 — Travel expense double-counting:** Of five business trips James took in 2025, three were employer-reimbursed (flights and hotels paid by Meridian Logistics) and only two were self-paid consulting trips. Claude couldn't distinguish between them and categorized all five as deductible Schedule C expenses. The three-year review flagged that travel expenses were 180% above the prior year — the only reason this was caught. **Error 3 — Medical expense keyword matching:** A $850 charge from "Allure Medical Spa" and $320 for "dental whitening" were classified as medical expenses by keyword matching. Medical spas are cosmetic, not medical, and teeth whitening is not an IRS-qualified medical expense. **Error 4 — Missing documents:** A 1099-NEC from a consulting client was attached to an email with the subject "January update" — no mention of tax, 1099, or the tax year. Claude's email search never found it. Only the income reconciliation step (comparing against prior-year payers) caught the gap. **Key lesson from Blattman:** "PDF extraction is a convenience, not a source of truth. Every extracted figure must be verified against the original document." The verification step is not optional — it's a mandatory gate.