How do I merge multiple excel files to a single excel file

So I was trying to make an excel sheet aggregator. In my line of work we get people who send us a bunch of individual excel files that are all related each with only 1 sheet used.

I was following to some degree this previous post's ideas. But upon doing so, some of the excel sheets I copied were coming up blank. Only certain ones. I have no idea why some are blank and others are fine.

Here is the code I use to open and copy the excel files

         OpenFileDialog browse = new OpenFileDialog();
            browse.Multiselect = true;
            DialogResult result = browse.ShowDialog();

            if (result == DialogResult.OK)

                try //try to open it. If its a proper excel file
                {   
                    excel = new Excel.Application();
                    excel.Workbooks.Add("");
                    finalized = excel.Workbooks[1];
                    excel.SheetsInNewWorkbook = 1;
                    for(int i=0; i< browse.FileNames.Length; i++)
                    {
                        excel.Workbooks.Add(browse.FileNames[i]);
                    }
                    //skip the first workbook as it is the finalized one
                    //also note everything in excel starts at 1 and not 0
                    for(int i=2; i<excel.Workbooks.Count; i++)
                    {
                        int count = excel.Workbooks[i].Worksheets.Count;
                        excel.Workbooks[i].Activate();
                        for (int j = 1; j < count; j++)
                        {

                            Excel._Worksheet pastee = (Excel._Worksheet)excel.Workbooks[i].Worksheets[j];
                            Excel._Worksheet sheet = (Excel._Worksheet)finalized.Worksheets.Add(Type.Missing, Type.Missing, Type.Missing, Type.Missing);
                            //Excel._Worksheet sheet = finalized.Sheets[1];
                            pastee.Copy(Before: sheet);


                        }//end of for j
                    }//end of for i
                }//end of try

Here is the code I use to save the excel file

            SaveFileDialog browse = new SaveFileDialog();
            browse.Title = "Save as Excel";
            browse.Filter = "Excel workbook | *.xlsx";
            DialogResult result = browse.ShowDialog();

            finalized.SaveAs(browse.FileName, Excel.XlFileFormat.xlWorkbookDefault);

            MessageBox.Show("Success", "Message");
            //unlock the file
            Global.releaseComObjects(finalized, excel);