AutoComplete filtering coorelated subquery

I am using ASP.Net Ajax Control Toolkit to populate 3 textbox controls. When any of these controls are used and a postback is performed ... the remaining 2 controls still have yet to be filtered or used. I want the remaining 2 source data to be a subset of the original data based off the control already used.

3 controls include: client name, employee, client number. If there are 100 total records and a user chooses an employee name when the postback is done I want the available choices of "client name" and "client number" to only show relevant / related content. (i.e. only the data where the employee exists).

I have created a BindData() method where I bind the datagrid based on values from the Ajax AutoComplete textboxes. I use a series of if-else if statements to determine which condition is true. So, following my example above, if a user selects an employee then in this BindData() method I populate that value to a label on the page (i.e. lblemployee.text ). I then use that lblemployee.text value to pass into my NEW page method.

Now on page_load() I create a series of if statements checking to see if any label controls contain content. So if the lblemployee.text != "" then I want to programmatically call a NEW page method to populate the 2 remaining, un-used controls instead of using the ORIGINAL page method which pulls all values for the specific field.

I hope I haven't confused or lost anyone ... so here is my code:

protected void Page_Load(object sender, EventArgs e)
        {
            if (!Page.IsPostBack)
            {
                if (lblClientName.Text != "")
                {
                    string myclname = lblClientName.Text;
                    txtClientName.Text = myclname;
                }
                if (lblAtty.Text != "")
                {
                    string myAtty = lblAtty.Text;
                    txtBillingAtty.Text = myAtty;
                    string prefixText = myAtty;
                    int count = 1;
                    FilterClientNumber(prefixText, count);
                }
                if (lblClientNum.Text != "")
                {
                    string myclnum = lblClientNum.Text;
                    txtClientNum.Text = myclnum;
                }
                // populate grid
                ClientFilterDataContext cfGrid = new ClientFilterDataContext();
                var queryGridCount = (from abc in cfGrid.myTable
                                    select abc).Count();
                lblRowCount.Text = queryGridCount.ToString(CultureInfo.InvariantCulture);
                lblRowCount.DataBind();

                var queryGrid = from b in cfGrid.myTable
                                select b;
                GridView1.DataSource = queryGrid;
                GridView1.DataBind();

            }
}

[System.Web.Script.Services.ScriptMethod()]
        [System.Web.Services.WebMethod]
        public static List<string> FilterClientNumber(string prefixText, int count)
        {
            using (SqlConnection conn = new SqlConnection())
            {
                conn.ConnectionString = ConfigurationManager
                        .ConnectionStrings["myConnectionString"].ConnectionString;
                using (SqlCommand cmd = new SqlCommand())
                {
                    cmd.CommandText = "select ClientNum from myTable where " +"employee like @SearchText + '%' order by ClientNum";
                    cmd.Parameters.AddWithValue("@SearchText", prefixText);
                    cmd.Connection = conn;
                    conn.Open();
                    List<string> customers = new List<string>();
                    using (SqlDataReader sdr = cmd.ExecuteReader())
                    {
                        while (sdr.Read())
                        {
                            customers.Add(sdr["ClientNum"].ToString());
                        }
                    }
                    conn.Close();

                    return customers;
                }
            }
        }

So what this page method is intending to do is since the employee has already been chosen when the postback occurs I need to fire off this page method with a new query using the employee as an additional filter so that my new result set of "client numbers" is only relating to this employee.