Welcome and thanks for dropping by the Community, @susan_akira.

To know more about the breakdown of the IIF files and why certain headers are used, I suggest posting this question to our Intuit Developers Community. It is a separate forum where product experts, engineers, and fellow developers share insights regarding software integration and application concerns.

Here’s how: 

1. Visit: https://help.developer.intuit.com/s/.
2. On the Intuit Developer page, hover your mouse cursor to API Docs & Tools.
3. Go to QuickBooks Desktop.

To learn more about importing and managing IIF files in QBDT, consider checking out these articles:

• IIF Overview: import kit, sample files, and headers.
• Tasks you can do with IIF files.
• Export, import, and edit IIF files.

Please let me know if you have any other questions by clicking the Reply button below. I'll be here to assist. Have a good one!