Maybe this is a known thing, but here's a DP for Amex Plat airline credit. Delta is my selected airline and I was less than $100 into the $200. We're flying Delta to Vegas in December so I figured we'd hit the Sky Club and maybe some in flight purchases, realizing I may not hit my $200 this year.
When I purchased my DH's ticket (I used skymiles for mine), he had a $100 credit from last year when a hurricane postponed our WDW trip and the new tickets in January were $100 cheaper. ANYWAY, the flight was like $203 (one way, we're doing SW back) so the charge to my Amex was $103 after his voucher. Anyway, Amex covered it toward the Delta $200 allowance! Nice surprise. I've got $13 left and should be able to use that easily.