You're running yourself in circles! I'll try to help as well
It doesn't matter when your anniversary is (unless you applied after May 2017 which you didn't), the travel credit resets at the end of the Dec statement cycle which for him will be Dec 17. You hopefully already got your double dip, or you're out of luck at this point. Your DH had the 2016 travel credit valid until approx Dec 17, 2016 and then he received the 2017 travel credit. Therefore the travel credit is tied to the mid-Dec statement close and not to when you pay the annual fee.
YOU are the one who has the double dip POTENTIAL left. You get your 2018 travel credit mid Dec & could use it and then cancel the card before the annual fee hits in Jan.