I'm looking to burn off some SWUs (plat benefit) on JFK-LAX and vice versa, but would like to know how successful folks have been using SWUs on this flight (when coded correctly, of course).

The K-fare flights are $200+ above the lowest current fare, and I'm afraid of purchasing the K-fare and not being able to use the SWU - and essentially donating $200 to Delta for no good reason.

Reading the other threads, I understand SWUs clear at the gate (since there's generally no advance availability) but that SWUs clear before complementary upgrades.

Have folks faced difficulties using a correctly coded SWU but unable to use them because the BE cabin was full?