I've had a response from Prof. McCarthy.
He's interested in the question, but has to say that, in all his years of study, he has never come across any original irish star-names in the medieval works.
I myself don't think this is the end of the story. It's all the more interesting to me, because it might suggest that the Greek names came over very early on.
Prof. McCarthy has offered to ask about.
More as comes to light.
Diane
".. the Carthaginian captain Hamilar saw in Birttany about 600bc .. skin boats which were making (so he reported) the three hundred mile crossing to the holy island of Ierne (Eire)"
  