Sag3, welcome to FlyerTalk!
If you didn't already know, the expiration date refers to when you
ticket your flight, and you can then take it up to a year later.
If you already knew this, I have two observations, which involve your choices or finding out more info: first, maybe using up the pseudo-money (getting value for what is otherwise worthless) could justify using our nice airport at CVG to connect?
Second: maybe you can use Delta $$ on Air France codeshares from London, or at least UK. I do not know about this. Others who might know should chime in shortly, I hope.
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"Service" should be a noun, not a verb.
Delta Flyers' Guide