This is our first year end with SAP. I found there are many BSI TUBs keep coming out to correct previous TUBs for calculating 2008 taxes. We already have 2 payroll periods ran in 2008, should we force retro back to calculate the tax in period 1 of 2008? I asked BSI this question and they told me I don't need retro calculation. But I still don't understand their explanation about how this works.