Counting on stars

[ReneZ]

Isn't there a conflict between the signs of the Zodiac in what might be something we would call astrology on the one hand, and named fixed stars on the other?

Not necessarily. The star catalogue of Ptolemy expressed one of the two position coordinates of a star (namely its longitude) as the combination: zodiac sign + degrees inside the zodiac sign (0-30).
This means that in works we would now call astronomical, the zodiac signs played an important role.
On the other hand, these works would not restrict themselves to the zodiac constellations. The medallions in the Voynich MS may be assumed to be more of astrological nature (in the modern sense).

Since one of the two stars in the Pisces sign has a label, and there are only 29 labelled nymphs around it, a valid possibility is that this should be considered as "one of the thirty". This possibility should not be ignored when trying to understand the meaning of these stars in the zodiac emblems.

Another possibility is that these stars in the emblems could be the planets.