Checking for duplicate values in datagridview against another datagridview

Question

Hi,
I have a C# application which connects to a SQL db.
On my new form I have three datagridview's.
dgv1 = populated by click event
dgv2 = populated when form opens via sql command
dgv3 = populated when form opens via sql command
I need to check if the value in cell 1 on dgv1 if there is a duplicate cell value in cell 2 on dgv2. (For each row of dgv1 against each row of dgv2)
If there is a duplicate value in cell 2 on dgv2, I need to get the value of cell 1 (which is the ID for that record) and add it to a list.
This list is to be used later to update a sql command, (which adds the ID of the duplicate record) then updates that particular record in the SQL db.

Here is the code I have composed so far, but it is not counting correctly.
I have been using the counter for testing to check if it is actually finding any duplicates. I have been entering at least one record in dgv1, that I know is in the database, but after the method has finished, it displays that it has not found any duplicates. Could some one help me finish this coding or atleast advise where I am going wrong here?

  public void btnCompareData_Click(object sender, EventArgs e)
  {
  if (!CheckedRows.Any())
  {
  // no labels to print; show error
  MessageBox.Show("No labels selected.", "Empty selection", MessageBoxButtons.OK, MessageBoxIcon.Warning);
  return;
  }
  else
  {
  DialogResult dr2 = MessageBox.Show("Are you sure you want to compare duplicate data.", "Compare", MessageBoxButtons.YesNo, MessageBoxIcon.Information);
  if (dr2 == DialogResult.Yes)
  {
 
  List<string> duplicateRecords = new List<string>();
  int dupCount = 0;

  foreach (DataGridViewRow row in dgv1.Rows)
  {
  foreach (DataGridViewRow row2 in dgv2.Rows)
  {
  if (row.Cells["col1"].Value == row2.Cells["col2"].Value)
  {
  duplicateRecords.Add(row2.Cells["ID"].Value.ToString());
  dupCount++; 
  }
  }
  }
  MessageBox.Show("Completed.\r\rDuplicate records updated: " + dupCount.ToString(), "Compare", MessageBoxButtons.OK, MessageBoxIcon.Information);
  }
  if (dr2 == DialogResult.No)
  {
  //cancel message, do nothing
  MessageBox.Show("Compare cancelled", "Compare", MessageBoxButtons.OK, MessageBoxIcon.Information);
  }
  }
  }
 
  //method to change the id in the sql command to update the record with the same ID
  public void updateRecords(string ID)
  {
  //get the ID, then add the id to the SQL command to update the record with that ID in the database
  string updateSQLRecord = "UPDATE tblAddress SET matchedDate = GETDATE() WHERE ID = '" + ID + "'";
  //now pass the sql string to update the duplicate records.(not finished here yet)
  }

When the method has finished, even if I have manually entered a value in dgv1 that I know is in dgv2, the counter still displays 0.
Please help :)