DL has never had that. At least not the last few years. I have been on a flight where every single BE seat but one was available - unsold, I saw it (was on the flight) all empty, and yet from some 330 days out up to an hour before flight (I checked a few times each week for a good 11 months), DL had it whited out and would refuse to sell an award seat at any price, at even the 4.5x of the normal price high level.

So, DL will rather have a plane fly out practically completely empty (only 1 seat in a cabin occupied), than offer an award seat to be booked.

The whiteout dates often will cover up to 3/4s of a month, even on routes with 3x daily flight, all the flights will be whited out for awards, while still there are well over 500 revenue seats waiting to be sold.