What is the absolute most authoritative source for factually verifying wages that have already been processed and paid to an employee?

Answer

The employer's internal payroll system or HRIS employee self-service portal.

While external tools are useful for estimation and comparison, the employer's internal systems are the final destination for factual verification of wages already paid, as they reflect the exact payroll processing records.

What is the absolute most authoritative source for factually verifying wages that have already been processed and paid to an employee?
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