Direct answer: A possible mismatch exists when the form, broker export, wallet history, acquisition records or tax software do not agree. The difference is a signal to compare records—not proof that the broker or taxpayer is wrong.
The four mismatch types
| Type | What disagrees | First record to compare |
|---|---|---|
| Proceeds | Form total vs. disposal export | Transaction-level sales/exchanges |
| Cost basis | Basis blank or different | Original purchase + fees |
| Transfers | Deposit appears without acquisition history | Sending-wallet/exchange record |
| Classification | Software treats activity differently | Import log + transaction type |
Why diagnosis matters
If proceeds are correct but basis is missing, asking the broker to “fix proceeds” wastes time. If basis is complete but software imported the same account twice, reconstructing purchase history does not fix the duplicate. Name the mismatch first.