With a bit of tweaking I got it to work. Thanks for all your help on this. This will save several people from pulling their hair out. I added a secondary filter to get rid of the header rows that were comiong over onto the Returns sheet. I was able to modify the formula in column A on the Jan-Dec sheets so that the code would handle it cleaner.
Here is the code that I ended up with.
Sub DetailConsolidation()
Dim WS As Worksheet, WS1 As Worksheet, WB As Workbook
Dim MyArray, x As Long
MyArray = Array("Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec")
Set WS1 = ActiveWorkbook.Worksheets("Returns")
For x = 0 To 11
Set WS = ActiveWorkbook.Worksheets(MyArray(x))
WS.Range("A1:N" & WS.Cells(Rows.Count, 1).End(xlUp).Row).Copy WS1.Cells(Rows.Count, 1).End(xlUp).Offset(1)
Next
If WorksheetFunction.CountIf(WS1.Range("C:C"), "GR for acc.assgt rev") > 0 Then
WS1.Range("A2", WS1.Cells(Rows.Count, "n").End(xlUp)).AutoFilter Field:=3, Criteria1:="GR for acc.assgt rev"
WS1.Range("A2", WS1.Cells(Rows.Count, 2).End(xlUp)).SpecialCells(xlCellTypeVisible).EntireRow.Delete
WS1.Range("A2").AutoFilter
End If
If WorksheetFunction.CountIf(WS1.Range("C:C"), "Vendor Material Number") > 0 Then
WS1.Range("A2", WS1.Cells(Rows.Count, "n").End(xlUp)).AutoFilter Field:=3, Criteria1:="Vendor Material Number"
WS1.Range("A2", WS1.Cells(Rows.Count, 2).End(xlUp)).SpecialCells(xlCellTypeVisible).EntireRow.Delete
WS1.Range("A2").AutoFilter
End If
If WorksheetFunction.CountBlank(WS1.Range("A1", WS1.Cells(Rows.Count, 2).End(xlUp))) > 0 Then
WS1.Range("A1", WS1.Cells(Rows.Count, 2).End(xlUp)).SpecialCells(xlCellTypeBlanks).EntireRow.Delete
End If
End Sub