IF function combination of COUNTIF function

Hi there,

I would like to seek help about my workbook file problem. here are the possible condition,kindly check my workbook.

1. IF the Doc Number are same and on the VAT TREATMENT column are all PASS then it will put on Comments column PASS.

2. IF the Doc Number are same and on the VAT TREATMENT column is all WARN then it will put on Comments column FAIL.

3.IF the Doc Number are same and on the VAT TREATMENT column one of it(Doc Number) is WARN,then it will put on Comments column FOR INVESTIGATION.

I just need Comments column to populate using macro VBA, I just put manually the "Should Be" answer. Somehow I don't know if I should use "IF AND" function with combination of COUNTIF. Kindly help me with this. Thanks a lot!