c# - Datagridview filled with datasource = {}

Question

I'm having the most crazy issue ever I have one tabcontrol where I add a tabpage then create a datagridview filling it with a query as datasource and make some visual changes on it and then make the same thing for another tabpage.

I run the code and somehow I get the data I want showing in the gridviews everything fine except the visual changes in the second one. I go debugging and end up finding out that the visual changes aren't happening because technically the query return the second datagridview gets as datasource is = {} so it has no rows to make visual changes on. but the data is showing on the datagridview anyway. I tried changing the order of the datagridviews and it was the very same issue, so I think it's something about the order the code is but I don't understand what nor where exactly.

I'm working on Visual Studio 2012 in C#, accessing the data of a Access 2010 file. And here is the code in question:

        ///Tabela por calibrar
        DataTable tabelaEqui = null;
        tabelaEqui = calibracaoBL.planoCalibracaoAtualCalibradosServico(DateTime.Now.Year, servico);
        DataGridView gridPorCalibrar = new DataGridView();
        gridPorCalibrar.DataSource = tabelaEqui;

        tabControl1.TabPages.Add(cbServico.Text + " - Por Calibrar");

        tabControl1.TabPages[0].Controls.Add(gridPorCalibrar);
        gridPorCalibrar.Dock = DockStyle.Fill;
        gridPorCalibrar.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.DisplayedCells;
        gridPorCalibrar.AutoSizeRowsMode = DataGridViewAutoSizeRowsMode.DisplayedCells;
        for (int i = 0; i < gridPorCalibrar.Rows.Count - 1; i++)
        {
            for (int j = 5; j < gridPorCalibrar.Rows[i].Cells.Count; j++)
            {
                string s = gridPorCalibrar.Rows[i].Cells[j].Value.ToString();
                Boolean b = !s.Equals("");
                if (b)
                {
                    gridPorCalibrar.Rows[i].Cells[j].Style.BackColor = Color.Green;
                }
            }
        }
        mudarCabeçalho(gridPorCalibrar);


        ///Tabela Calibrados
        DataTable dt = null;
        dt = calibracaoBL.planoCalibracaoAnosAnterioresServico(DateTime.Now.Year, servico);
        DataGridView gridCalibrados = new DataGridView(); // here I got check and dt = {}
        gridCalibrados.DataSource = dt;

        tabControl1.TabPages.Add(cbServico.Text + " - Calibrados");

        tabControl1.TabPages[1].Controls.Add(gridCalibrados);
        gridCalibrados.Dock = DockStyle.Fill;
        gridCalibrados.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.DisplayedCells;
        gridCalibrados.AutoSizeRowsMode = DataGridViewAutoSizeRowsMode.DisplayedCells;
        for (int i = 0; i < gridCalibrados.Rows.Count - 1; i++)
        {
            for (int j = 5; j < gridCalibrados.Rows[i].Cells.Count; j++)
            {
                string s = gridCalibrados.Rows[i].Cells[j].Value.ToString();
                Boolean b = !s.Equals("");
                if (b)
                {
                    gridCalibrados.Rows[i].Cells[j].Style.BackColor = Color.Green;
                }
            }
        }
        mudarCabeçalho(gridCalibrados);

Here is the first one:

Here is the second one:

UPDATE in response to @varocarbas :

I'm checking the datasource is blank in two points. Point one: dt = calibracaoBL.planoCalibracaoAnosAnterioresServico(DateTime.Now.Year, servico); // that method that runs a query returns {}. But the query itself is not the issue since it works just fine, it's working perfectly when I try it elsewhere.

Point two: DataTable dt = null; dt = calibracaoBL.planoCalibracaoAnosAnterioresServico(DateTime.Now.Year, servico); DataGridView gridCalibrados = new DataGridView(); // here I go check the dt variable and shows dt={}

The code goes into the for (int i = 0; i < gridCalibrados.Rows.Count - 1; i++) but since gridCalibrados.Rows.Count = 0 it skips the loop.

Here is the method mudarCabeçalho

    public void mudarCabeçalho(DataGridView grid)
    {
        for (int i = 5; i < grid.ColumnCount; i++)
        {
            string[]  s = grid.Columns[i].HeaderText.Split('-');
            switch (s[1])
            {
                case "01":
                    grid.Columns[i].HeaderText = "Jan";
                    break;
                case "02":
                    grid.Columns[i].HeaderText = "Fev";
                    break;
                case "03":
                    grid.Columns[i].HeaderText = "Mar";
                    break;
                case "04":
                    grid.Columns[i].HeaderText = "Abr";
                    break;
                case "05":
                    grid.Columns[i].HeaderText = "Mai";
                    break;
                case "06":
                    grid.Columns[i].HeaderText = "Jum";
                    break;
                case "07":
                    grid.Columns[i].HeaderText = "Jul";
                    break;
                case "08":
                    grid.Columns[i].HeaderText = "Ago";
                    break;
                case "09":
                    grid.Columns[i].HeaderText = "Set";
                    break;
                case "10":
                    grid.Columns[i].HeaderText = "Out";
                    break;
                case "11":
                    grid.Columns[i].HeaderText = "Nov";
                    break;
                case "12":
                    grid.Columns[i].HeaderText = "Dez";
                    break;

            }
        }
    }