Hi Scott,

Thanks for the rep points. It's my pleasure to help, especially for someone who is trying to learn to fish.

I was able to find out the cause of some of your problems, but not the reason why the problem occurs.

...showed a problem wherein only the first textbox value associated with the comboboxes posts to the spreadsheet. That problem persists.
1. For some unknown reason the ComboBox .ListIndex value always had the value -1, even when ComboBoxes had lists in them. When I changed the test from .ListIndex to looking for the value in the ComboBox I had success. Your test for the first ComboBox always tested for the VALUE.

2. The use of 'Option Explicit' at the top of each code module is highly recommended. To prevent typos from ruining days and weeks of work 'Option Explicit' is NEEDED at the top of each code module. This prevents errors caused by missspellings and FORCES every variable to be DECLARED (e.g. dim i as Integer).
http://www.cpearson.com/excel/DeclaringVariables.aspx

Important excerpts of the code I used from Sub xxx follow:

Dim RowCount As Long
Dim response As Long

If Len(Trim(CbAllocate1.Value)) = 0 Then
    Exit Sub  ' nothing selected
  End If
    
  Set tbl = Sheets("Data").ListObjects(1)
  Set col = tbl.ListColumns(CbAllocate1.Value)
  Set findheader = col.Range
  Sheets("Data").Cells(Rows.Count, findheader.Column).End(xlUp).Offset(1).Value = TbSplit1.Value
    
  If Len(Trim(CbAllocate2.Value)) > 0 Then
    Set tbl = Sheets("Data").ListObjects(1)
    Set col = tbl.ListColumns(CbAllocate2.Value)
    Set findheader = col.Range
    Sheets("Data").Cells(Rows.Count, findheader.Column).End(xlUp).Offset(0).Value = TbSplit2.Value
  End If

If Len(Trim(CbAllocate3.Value)) > 0 Then
    Set tbl = Sheets("Data").ListObjects(1)
    Set col = tbl.ListColumns(CbAllocate3.Value)
    Set findheader = col.Range
    Sheets("Data").Cells(Rows.Count, findheader.Column).End(xlUp).Offset(0).Value = TbSplit3.Value
  End If
  
  If Len(Trim(CbAllocate4.Value)) > 0 Then
    Set tbl = Sheets("Data").ListObjects(1)
    Set col = tbl.ListColumns(CbAllocate4.Value)
    Set findheader = col.Range
    Sheets("Data").Cells(Rows.Count, findheader.Column).End(xlUp).Offset(0).Value = TbSplit4.Value
  End If
        
  If Len(Trim(CbAllocate5.Value)) > 0 Then
    Set tbl = Sheets("Data").ListObjects(1)
    Set col = tbl.ListColumns(CbAllocate5.Value)
    Set findheader = col.Range
    Sheets("Data").Cells(Rows.Count, findheader.Column).End(xlUp).Offset(0).Value = TbSplit5.Value
  End If
        
  If Len(Trim(CbAllocate6.Value)) > 0 Then
    Set tbl = Sheets("Data").ListObjects(1)
    Set col = tbl.ListColumns(CbAllocate6.Value)
    Set findheader = col.Range
    Sheets("Data").Cells(Rows.Count, findheader.Column).End(xlUp).Offset(0).Value = TbSplit6.Value
  End If
I will address the questions you raise inside your sample file in the following post.

Lewis