Originally Posted by
Goldorak
the problem is that there is nothing written here and FB is replying as per their own rules. The basis of my previous answer to your question was based on the fact that, when purchasing a paid upgrade in advance on DL flights, the ticket is reissued with the new booking class/fare, hence the FFP credit as per the upgraded class rule.
My understanding is that DL only reissues the ticket if all flights on a fare component (e.g. both DEN-ATL and ATL-SCL) are upgraded with cash. If only one is upgraded, it's basically buying a seat assignment, though DL does by a side process give SkyMiles elite credit for going up a cabin.
Reissuing also means you're more likely to keep the upgrade in schedule changes (vs. getting a refund).
For Y -> PE, this is a problem when you have a domestic connection, of course.