I certainly have sympathy with the frustrations you’ve experienced, and I agree that some more structured tutorial content could be very helpful here. I’ll discuss this with John and Anthony and see whether we can together come up with something that will provide the information you need.
In the meantime, if you are finding that your own playback techniques aren’t working but the built-in ones are, there are two things I can think of, off the top of my head, that could perhaps help.
The first concerns mutual exclusion groups. When you define your own playback techniques, Dorico doesn’t know anything about the nature of the playback technique you’re creating: it doesn’t know whether it can be applied on top of another technique that is already active, or it needs to be used as an alternative. For example, pizz. and arco are exclusive, while con sord. could (in principle) be applied whether the instrument is currently being plucked or bowed, subject to the virtual instrument supporting it – but Dorico doesn’t “know” this, and particularly when you define your own playback techniques, it may be obvious to you or me whether or not you can add them together or whether you must switch between them, but it won’t be obvious to Dorico.
So the first thing to check is that the playback techniques you have created are, if necessary, contained within a mutual exclusion group in your expression map, assuming they are indeed exclusive.
The second thing to check is that you have got the appropriate connection between the playing techniques that appear in the score and the playback techniques that they trigger in the world of playback, and that the right playback techniques are referenced in your expression maps.
For example, you have created a playback technique (in Library > Playback Techniques) for “Pattern Legato”. To trigger this in playback, you also need a playing technique (in Library > Playing Techniques) that has a suitable appearance in the music (e.g. just some text, “Pattern Legato”, would do, and you can later on hide the playing technique via the Properties panel if you don’t want to see it printed in the music) and has the appropriate playback technique chosen in the Playback technique menu.
Possibly one of these two things – the playback technique referenced in the expression map, or the playback technique referenced by the playing technique that you actually create in the music to trigger the technique change – is not hooked up correctly.
(I know the similarity in terminology between playing techniques and playback techniques is hugely unhelpful, and we certainly don’t rule out making some changes in this area to try to make the relationship clearer.)
I hope this provides you with some initial pointers. Do let me know if you’re still not getting anywhere.