The reason the legacy option was added to the standard reports was because in the past those reports would always fetch the fare amount from the “Price paid” column in the Job-editor (here: https://admin.taxicaller.net/admin/jobs/jobeditor.php)
The new default reports fetch the price from the receipt which is also found in the job editor, but is not editable (because if it were editable it wouldn’t really be a receipt).
If you for some reason would have to change the price of a job and would like to use this report the legacy option is there so that you can edit the amount on whichever job that has an incorrect amount.
Short summary The reason legacy reports could show a different price is because they fetch the fare from the job-editors “Price paid” column (which you can edit manually), while the default reports fetch it from the receipt (this one you cannot edit).