Okay, well I don't have a lot of refunds, but I poked around a bit.
Where I did a full refund there is a 0 (zero) in the fields. Meaning the adjusted totals equals zero. Where there was no adjustment the cells are empty with no entry.
So if you did a full refund it should have zero, if there was nothing done to an order it is empty, partial refunds show totals (original amount -refund amount).
On my partial refund the original order total was $17.00. I refunded $5.00 for shipping overage so the adjusted order total showed the amount of $12.00. It doesn't show what you refunded, just the final amounts after adjustments.
I don't know how coupons factor in to any of that because I don't have any transactions that have coupons used.
I have a habit of downloading all the CSV files monthly, but for end of the year purposes downloaded the CSV files for the year. Because-- say I had an order in November and download my Nov CSV file on Dec. 1st, then refund that November order on Dec. 12 it can't show on the Nov. CSV I downloaded on Dec. 1st. So, if you are working off of "old" CSV files you may have some missing.
I checked all my shops total for the year I have a handful of partial and full refunds and the are all reflected in the order CSV I downloaded for the year.
The reasons your data could be wrong:
old file (sale in one month refund in a different month after you downloaded the file).
The file could be corrupted. Try re-downloading the file.
If you are importing the CSV file into a spreadsheet program it may not be importing the data properly. Some spreadsheet programs are better than others, although I have not seen any reports anywhere about Etsy files not importing correctly.