So, I've noticed that DL seems to zero out availability 2-3 days before the flight. For instance, I noticed a Sat flight MSP-MCO was F8A7 (which would correspond to what NWA-ers used to know as P8F7). Then, yesterday it zeroed out to F0A0.

Now, it is possible that the flight sold out, but the rest of the class availability also zeroed out (i.e. Y0B0H0 etc).

Is this something DL does different from NW? Primarily, I used to watch PxFx for chances of UG but with DL zeroing it out I can't imagine that the seats are really sold. Does DL do this to sell UG's? Perhaps the inventory management practices T-3 days is much different.

Any thoughts?