Do you have leading zeros in your import files? If so, re-opening a Comma Delimited (.CSV) file in Microsoft Excel will drop leading zeros at the beginning of any given column. If this happens, re-open the file and do the following:
1. Select the column header (A,B,C,...), for the column that has the leading zeros, to highlight the entire column
2. Right-Click on the column header
3. Select 'Format Cells'
4. Select the 'Number tab'
5. In the 'Category' list, click 'Custom'
6. In the 'Type' box, replace the word 'General' with the number format, such 00 for a two-digit code, or 0000000 for a seven-digit code.
This will reset the leading zeros (that Excel initially stripped off) when the file is saved again as a .CSV type.
Warning: Do not re-open the file or the zeros will get removed again.
Video - How to Work with Leading Zeros