So to clarify what is tested as part of a parallel run, the parallel run is a test of the payroll build (so the data, YTD data, paycodes, working patterns, payroll rules etc that client provided to provider so to build the payroll) via running a payroll at a point in time (e.g. September 2024).
This means that client´s YTD data influences provider´s September 2024 payroll results so they can be compared with the current provider´s September 2024 payroll results.
Otherwise it would be as if provider ran the payroll at the start of the tax year when there is no YTD data (e.g. January 2024) and compared it with September 2024 from the current provider that has YTD data.
This would mean that payroll differences between January 2024 and September 2024 would be due to a lack of YTD data.
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