If when uploading Vantiv residuals you are take to the page listing new merchants that will be added but the merchants are already in IRIS, it's possible that the MIDs in your file were rounded.
Open the file and see if the MID is shortened or rounded. If all accounts look like they have the same short MID, then that indicates the file was opened and saved after it was downloaded.
Note that in Vantiv residuals files, each account has multiple rows, so it's likely that the first several rows will have the same MID, and then the next several rows will have the same new MID, and so on. That is expected.
A typical Vantiv MID is like 520001234567 but they can vary.
At first it may show the MID's (in column named MERCH_NBR) as something like 5.2E+11. And even after you re-format the cells to be Number, it will look normal but they won't be unique, i.e., they are rounded.
If the file has all the MID's shortened and the full number can not be shown, have the client re-send us the file but unopened and unsaved after it was downloaded from Vantiv. We only use the MerchDetail file for each month.