Convert string to datetime

This is a favorite function I used a lot when getting data from remote systems. For example I once needed to retrieve data from an AS/400 box, and the file format was already specified. However, date fields in the file could look pretty different (6, 8, 10 digits with or without delimiters between year/month/day), depending on certain aspects so my timesaving all-purpose reoutine for getting date values look like this: 

 public static DateTime GetDateValue(string sVal)

    {

        DateTime dtRet;

        try

        {

            int nAdd = 1900;

            if (Convert.ToInt32(sVal.Substring(0, 2)) < 80)

                nAdd = 2000;

            if (sVal.Length == 6)

            {

                //YYMMDD

                dtRet = new DateTime(nAdd + Convert.ToInt32(sVal.Substring(0, 2)), Convert.ToInt32(sVal.Substring(2, 2)), Convert.ToInt32(sVal.Substring(4, 2)), 0, 0, 0);

                return dtRet;

            }

            if (sVal.Length == 8)

            {

                if (sVal.IndexOf("-") > 0)

                {

                    //YY-MM-DD

                    dtRet = new DateTime(nAdd + Convert.ToInt32(sVal.Substring(0, 2)), Convert.ToInt32(sVal.Substring(3, 2)), Convert.ToInt32(sVal.Substring(6, 2)), 0, 0, 0);

                    return dtRet;

                }

                //YYYYMMDD

                dtRet = new DateTime(Convert.ToInt32(sVal.Substring(0, 4)), Convert.ToInt32(sVal.Substring(4, 2)), Convert.ToInt32(sVal.Substring(6, 2)), 0, 0, 0);

                return dtRet;

            }

            if (sVal.Length == 10)

            {

                //YYYY-MM-DD

                dtRet = new DateTime(Convert.ToInt32(sVal.Substring(0, 4)), Convert.ToInt32(sVal.Substring(5, 2)), Convert.ToInt32(sVal.Substring(8, 2)), 0, 0, 0);

                return dtRet;

            }

            return Convert.ToDateTime(sVal);

        }

        catch (Exception){}

             
             dtRet = new DateTime(1900, 01, 01, 0, 0, 0);

        return dtRet;

    }

protected void Page_Load(object sender, EventArgs e)
    {       
        textBox1.Text += "010102->" + GetDateValue("010102").ToString("yyyy-MM-dd") + Environment.NewLine;
        textBox1.Text += "790102->" + GetDateValue("790102").ToString("yyyy-MM-dd") + Environment.NewLine;
        textBox1.Text += "800102->" + GetDateValue("800102").ToString("yyyy-MM-dd") + Environment.NewLine;
        textBox1.Text += "810102->" + GetDateValue("810102").ToString("yyyy-MM-dd") + Environment.NewLine;
        textBox1.Text += "20000102->" + GetDateValue("20000102").ToString("yyyy-MM-dd") + Environment.NewLine;
        textBox1.Text += "01-01-02->" + GetDateValue("01-01-02").ToString("yyyy-MM-dd") + Environment.NewLine;
        textBox1.Text += "79-01-02->" + GetDateValue("79-01-02").ToString("yyyy-MM-dd") + Environment.NewLine;
        textBox1.Text += "80-01-02->" + GetDateValue("80-01-02").ToString("yyyy-MM-dd") + Environment.NewLine;
        textBox1.Text += "810102->" + GetDateValue("81-01-02").ToString("yyyy-MM-dd") + Environment.NewLine;
        textBox1.Text += "2000-01-02->" + GetDateValue("2000-01-02").ToString("yyyy-MM-dd") + Environment.NewLine;
       
    }

Here is the .aspx file ::

Output::

010102->2001-01-02
790102->2079-01-02
800102->1980-01-02
810102->1981-01-02
20000102->2000-01-02
01-01-02->2001-01-02
79-01-02->2079-01-02
80-01-02->1980-01-02
810102->1981-01-02
2000-01-02->2000-01-02