I was wondering that too. But I think if it’s within 1 day, it should be fine
You are right.
I purchased delta comfort to trigger airline credit, then when i called to cancel my flight the agent said seats aren't refundable When i asked since when is this policy in place he wouldn't answer me. Bur turns out, besides for being arrogant and weird, he was thankfully clueless, bc a day later i was credit for the ticket as well as the extra charge for the comfort seat.