Right, I try summarising again, “sub voices” (above) was my terminology. I am deep learning here, this is why I am so finicky 
Let me instead call the voices 1u (voice 1 up-stem) 1d (Voice 1 down-stem), 2u(Voice 2 up-stem), 2d, 3u, 3d. etc..
Important note Flipping the stem of a note, does not change it’s voice. Therefore, a visually upstem note can be part of a “down- stem” voice.
To accurately identify which voice a note is in:
To properly identify what note a voice is in, click on the note, highlighting it in orange, then, whilst ensuring Dorico is full screen, look at the status bar (bottom horizontal panel) and it will say “Down Stem Voice 2”. When note input is activated, the carat also indicates which specific voice you are in. It only scrolls through the voicings you have previously used. If you have not used voice 3d, it will not show it. If you create a voice 3 D (using SHIFT V) then it will show is the scrolling.
Shift + V creates a new voice
V scrolls through the voices
To see voicings in different colors (in Dorico 6), Go to View/View Options, then highlight View Colors. Realise that the color of any voice, is changed to orange once it is selected. Therefore to see what voice color it is unselect it.
Correcting wrongly voiced notes
If you enter a note(s) into the wrong voice, you can change it by highlighting the notes in orange, then pressing the V key a number of times. This scrolls through the voicings you have made available. *As you do this, keep an eye on the status bar (Dorico in full screen), it will say which voice you have scrolled to. It’s a bit disconcerting to see the screen notation jump around, whilst you scroll through the wrong voicing options to find the correct one, but if you have notated your note correctly for that voice, then Dorico should get things into order.
The specific voicing selection (e.g. 2u) is shared throughout a staff (and presumably through out the the whole “part”). So if you enter some notes on bar 1 in voice 2u, then in bar 56, you again use voice 2u, you are using the same voice. However in the lower zone property menu, for any given note, there is “starts voice” and “ends voice” options. Not sure why?
I think there is no way to see the notes of only one voice of a staff in Dorico? (“View only voice 2d” - so to speak). Yet?
If you want to remove rests, perhaps to clean up eye clutter, then select the rest(s) you want to delete and go to Edit/Remove Rests. This removes only the rests you have selected.
If you want remove an unused voice. Close Dorico and restart. Dorico removes empty voices.
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