Invalid Product codes on product CSV import

-- HikaShop version -- : 4.4.1 (build 21-03-24)
-- Joomla version -- : 3.9.25
-- PHP version -- : 7.4.15
-- Browser(s) name and version -- : Firefox 86.01

After I import from CSV file I get an on-screen "Notice" and "Message" after the import that reports various things that either worked or failed. Is there any way of seeing in more detail what has failed? Like what are to 40 invalid product codes? --See attached pic. Which column in the import CSV file is the product code? The text in the 'product_code' column looks ok (but with lots of '_' inserted). Since I did not generate this text could I delete all this column text and import again?

Thanks

That's fine, the numbers work out.

Do the columns in the import CSV need to be in the same order as outputted? I'd like to relocate a few columns to the row start for a 3rd party to update details easily without having to scroll around lots. Can I leave them in this changed order or do I have to return them to their original positions before importing?

Also, what happens if there are some columns missing? Do they all need to be there? I know I can leave some blank.