It worked for one-way domestic fares as recently as November 26th, when I snapped up a cheaper Monday Thanksgiving return flight with the BfB discount. But then BfB was not showing on the 28th when the price dropped further (even for a new booking). But the new price was both good for different flight that we preferred anyway, and the non-BfB price was lower than I'd paid so I just did a change flight.

Disappointing if this has changed; with my family in multiple places we often have to combine in different ways and I much prefer to book one-way flights for all the common reasons. But good to know to check at least.