Excel 2007 : Fill gap between dates

Try this in the workbook module

Option Explicit

Private Sub Workbook_Open()
    Dim LastRow As Long, RowNo As Long

    With Sheets("Sheet1")
        LastRow = .Range("A" & Rows.Count).End(xlUp).Row
        If .Range("A" & LastRow) < Date - 1 Then
            If .Range("A" & LastRow).Offset(0, 1) = "" Then
                .Range("A" & LastRow).Offset(0, 1) = .Range("A" & LastRow).Offset(-1, 1)
                .Range("A" & LastRow).Offset(0, 2) = "Automated Entry"
            End If
            For RowNo = LastRow To LastRow + Date - .Range("A" & LastRow) - 1
                If .Range("A" & RowNo + 1) = "" Then
                    .Range("A" & RowNo + 1) = .Range("A" & RowNo) + 1
                    If .Range("A" & RowNo + 1) <> Date Then
                        .Range("A" & RowNo + 1).Offset(0, 1) = .Range("A" & RowNo + 1).Offset(-1, 1)
                        .Range("A" & RowNo + 1).Offset(0, 2) = "Automated Entry"
                    End If
                End If
            Next

        End If
    End With
End Sub

When you open this demo with macros enabled it will automatically add the missing data.
To test
Delete the last few rows (A:C) save the workbook, close, and reopen.
then
Delete the last few rows (A:C) plus what becomes the last row Column B, save the workbook, close, and reopen

Note: This will not fill missing entries in old sheets with missing data, it will only work from the last entered date forward.