I suspect I might conditionally merge those fields that could be empty to add unique text instead e.g.
{ IF { MERGEFIELD SS_1 } = "" "BLANK" "{ MERGEFIELD SS_1 }" } etc.,
then run a macro to remove the rows that contain 'BLANK' in the first column e.g.
If you use
https://www.gmayor.com/email_merge_addin.html to merge the documents, you can run the following macro from the process to remove the blanks on the fly.
Code:
Sub DelBlanks(oDoc As Document)
Dim oTable As Table
Dim iRow As Integer
Dim oCell As Range
Set oTable = oDoc.Tables(1)
For iRow = oTable.Rows.Count - 21 To 5 Step -1
Set oCell = oTable.Cell(iRow, 1).Range
oCell.End = oCell.End - 1
If oCell.Text = "BLANK" Then oTable.Rows(iRow).Delete
Next iRow
End Sub