Transactions are separated by whether basis was reported to the IRS by the broker, which is what the covered and non-covered distinction on form-1099-b means. Adjustment codes are entered here, including code W for a disallowed wash-sale-rule loss and codes for basis corrections.
Accuracy matters most where the broker's reported basis is wrong, typically for transferred positions, inherited or gifted shares, or securities acquired before basis reporting began. The correct approach is to report the broker figure and adjust, not to silently substitute your own.
Traders with high volume rely on software that imports broker data, but the wash sale calculation across accounts and across substantially identical positions is precisely where automated imports go wrong.
General information for the United States, not tax advice. Rules change and depend on your circumstances; confirm with a qualified adviser.
Related: schedule-d, form-1099-b, wash-sale-rule, cost-basis-methods, capital-loss-carryover