Daniel and all, sorry but I’m extremely unhappy with this. Your swing playback basically just doesn’t work and Dorico doesn’t reopen scores in the way that you last saved them.
Every time I close Dorico and reopen my score, all of the Playback Start Offsets get reset to “straight” for those notes to which I had applied a Playback End Offset to shorten the duration for my swing notation.
When I enter the Playback End Offsets, as discussed earlier, Dorico forces the off-beat notes back to the 50% point, making them straight. To get rid of this, one has to toggle Playback Start Offset on and off again for those notes (or for a whole passage). This makes the position go back to the swung position and results in proper playback. This toggling is a nuisance but not the end of the world.
What is the end of the world is finding that closing a reopening a score obliges one to start all over again and toggle all the notes’ Start Offsets.
This is the equivalent of Sibelius forcing a zero to “Live Start Positon” for every note that I put a “Live Duration” value to, every time I reopen a score. Which it doesn’t do, thankfully.