Not that another DP is needed, but here it is anyway:

12/14 purchased $150 GC on the mobile site which activates the GC after 24 hours
12/15 called for $259 fare which charged as $109 after GC, $109 showed as additional collection
12/19 Meter showed credit used
12/20 Credit posted

12/14: Purchased $256 RT ticket using $50 Delta GC (from last year's benefits) and Amex plat, posted as "additional collection" of $206.
12/18: $200 airline credit posted.

Thanks for all the info shared here.

Am I correct in assuming that I can't specify how much of a large balance gift card to use? I bought one of those $1000 DL gift cards from Costco (10% off). I'd like to use it in 2020 for an additional collection split tender, but don't think there's a way. Maybe on the phone?

I just booked a flight (literally this morning) with 3x$50 gift cards (so lower amount) - it did not let me specify an amount to use - made the gift card balance go to $0

See posts 2525 & 2527. We need a test volunteer :)

and #2530 for an alternative approach.

correct, after using some miles to bring the balance below $250 i used the card to pay the rest, triggering the credit

Come 2020 I will report my results then.

Amex Platinum - Delta comfort+ (success)
 

Here's a data point that worked (manually):

I booked a flight and then bought comfort plus on a separate transaction for $148. It did not trigger but was fairly easy to get amex to approve it for the airline credit. Be careful with Delta because they seem to use the word "upgrade" a lot. In a small crj, they actually use the term "upgrade to preferred" just to choose and pay for the exit row. This transaction was categorized as an upgrade, which is why it didn't trigger. When calling, never use the word upgrade but stress that it's just a "seat selection" and it's in the same cabin and class.

Dec 3: Posted transaction of $148 (labeled "upgrade")
Dec 10: I call for inquiry. He said that they have to wait 4 weeks. Since it's close to the end of the year, that they will do it in 2 weeks. He made a note on my record that said to call back after 2 weeks of the posted transaction and they will honor the credit.
Dec 18: I call back. She said that they really should wait for the 4 weeks but she was very nice and did it anyway.
Dec 19: Gauge moved.
Dec 20: Airline credit posted for $148!

I'm sure this has been answered but I couldn't find it!

Does anyone know if a charge that posts in 2019 will definitely count towards your 2019 credit? I will be flying Delta on 12/29 and was planning on using my last ~$25 for skyclub access for my wife. Thanks!

Bought the mileage booster for $59 x 2 and got $118 credit on my Amex. At least you can use the credit for extra miles, however I had to cancel my trip last minute...that's a different story. Waiting to see if luggage also gets a credit as I haven't hit my $200 limit yet. Cancelling the card tomorrow, the $500 fee just isn't worth the hassle to use these impossible to use credits.

Does anyone have any data points about purchasing award flights using skymiles and having the taxes refunded? my annual fee just hit a few days ago and i have until Jan 8 to get the full $595 refund. I was thinking about purchasing this award flight that has a $150 copay on Jan 1st, and hope it posts by Jan 6 or 7 and immediately cancel the card

Even if this does work what are the chances of this posting before the jan 6-7 due date?

In the past amex platinum refunded skymile award taxes but its been a while dunno if this has changed.

You could always buy a ~$1200 ticket. :p

Here's my experience:
12-16- Purchased $50 DL gift card from Target.com (language there says up to 24h to activate, better than the 3d @ it can take per DL agents [and per FT posts])
12-17- Purchased a $270 fare with $50 GC and $220 charge to Aspire; posted $220 as pending immediately
12-18- still pending
12-19- no longer pending but no credit showing
12-20- no longer pending but no credit showing
12-21- $220 credit showed up; have $30 left over

My two award tickets of $80 each were reimburse earlier this month.