I think I would probably be inclined to add a macro to the summary that would grab the data and formatting from the source documents and optionally run it when the document is opened. Add the following code and save the document as a macro enabled document. The macro assumes all three documents will be in the same folder.
http://www.gmayor.com/installing_macro.htm
Code:
Sub UpdateSummary()
Dim oSourceA As Document
Dim oSourceB As Document
Dim oTarget As Document
Dim oTable As Table
Set oTarget = ThisDocument
Set oTable = oTarget.Tables(1)
Set oSourceA = Documents.Open(FileName:=oTarget.Path & "\" & "Dept A - detail.docx", AddToRecentFiles:=False, Visible:=False)
Set oSourceB = Documents.Open(FileName:=oTarget.Path & "\" & "Dept B - detail.docx", AddToRecentFiles:=False, Visible:=False)
oTable.Cell(2, 3).Range.Text = oSourceA.Tables(1).Cell(2, 6).Range.Text
oTable.Cell(2, 3).Shading.BackgroundPatternColor = oSourceA.Tables(1).Cell(2, 6).Shading.BackgroundPatternColor
oTable.Cell(3, 3).Range.Text = oSourceA.Tables(1).Cell(3, 6).Range.Text
oTable.Cell(3, 3).Shading.BackgroundPatternColor = oSourceA.Tables(1).Cell(3, 6).Shading.BackgroundPatternColor
oSourceA.Close 0
oTable.Cell(2, 4).Range.Text = oSourceB.Tables(1).Cell(2, 6).Range.Text
oTable.Cell(2, 4).Shading.BackgroundPatternColor = oSourceB.Tables(1).Cell(2, 6).Shading.BackgroundPatternColor
oTable.Cell(3, 4).Range.Text = oSourceB.Tables(1).Cell(3, 6).Range.Text
oTable.Cell(3, 4).Shading.BackgroundPatternColor = oSourceB.Tables(1).Cell(3, 6).Shading.BackgroundPatternColor
oSourceB.Close 0
Set oSourceA = Nothing
Set oSourceB = Nothing
Set oTarget = Nothing
Set oTable = Nothing
End Sub
Sub AutoOpen()
UpdateSummary
End Sub