They are referring to the fact that Comfort Basic fares are not eligible for comp Medallion upgrades to First -- https://news.delta.com/introducing-d...ience-unpacked



Of course, if you are a Plat or Diamond, these fares hold little appeal as you are eligible for comp Comfort upgrades at purchase time. For the most part, DL does not seem to hold back Comfort seat inventory from SU comp upgrade bucket (although there seems to be a few reports where this may be happening). Although note that in some cases, Comfort Basic fares can be lower than corresponding Main Classic fares on routes (as below). Change/Cancel fees on Comfort Basic are the same as Main Basic ($99 domestic/short-haul international, $199 long-haul international).

I'm noticing they only seem to offer these fares for cheapest X/V fare classes on routes. When there is only Y/B/M/H/Q/K/L/U/T inventory open, they don't have Comfort Basic fare filings for those classes and your only Comfort fare option is Comfort Classic.


This is an example of a flight where there is only T class and higher inventory open and DL does not have T basis or higher Comfort Basic fares on route.