As a 'cellist, I’d like to mention that the thumb position should be considered part of the fingering. The thumb symbol (a zero digit with a little vertical stroke on the bottom) should be treated like any other fingering digit. I mention this because I found that in SMuFL the thumb symbol (U+E624, stringsThumbPosition) is located in the ‘String Techniques’ range (section 4.52), and not in the ‘Fingerings’ range (U+ED10-ED2F, section 4.115). I hope you are not overlooking it.
(Obviously, applying the thumb is definitely also a technique, but that is basically true for every finger…)
Open strings (ordinary zero) are part of the fingering too, but no doubt that is already accounted for, since it is in the SMuFL Fingering range.
BTW, In SMuFL, the fingerings 1-2-3-4-5 are described as ‘thumb’, ‘index finger’ etc. This is not true for string instruments, where 1 is the index finger, 2 is the middle finger etc., and 5 is not in use. (But I doubt it is worth a new SMuFL version to add that to the glyph descriptions 
Harmonics can be indicated with a small circle (in Dorico they are), but many editions use the open-string 0 digit (i.e. the typographically digit-like glyph) for harmonics as well. It looks like, and behaves as a fingering, and in a way it is, because it’s a way of applying a finger, touching the string lightly instead of pressing it. In general, for the player it’s always clear whether a zero indicates an open string or a harmonic. In the rare cases where this is ambiguous you may add the string number.
Elaine Gould uses circle-based symbols both for harmonics and thumbs. Some editions use the circle as the indicator of open strings as well, but to me that looks wrong. It depends on the edition whether the thumb symbol is represented by a circle with a stroke (may be more modern, see Gould) or a zero with a stroke (may be more traditional). Because the thumb is a finger, I prefer the tailed zero. It makes the fingerings typographically similar and easier to read as such. Maybe it should be a stylistic preference?
Note that a thumb can also play harmonics, for which the fingering is a combination (vertically stacked) of the thumb symbol and the harmonic 0/circle.
I don’t think there is a clear rule whether a harmonic 0 is on top or bottom if it’s combined with a finger.
HTH. I’m very happy with Dorico, and thrilled to see how fast it is becoming very, very good.
Peter Bouma, Amsterdam