No news is, well, no news in this case.
I've gone on a rampage to find any instances of data cards in Star Trek where they have a half bullnose edge. I haven't been able to find a single instance. I have found lots of instances of full bullnose edges, however. So at this point I'm skeptical that there actually were any half bullnose edge discs--despite people having "original Star Trek discs" that they swear have all kinds of trustworthy provenance.
Nevertheless, a lack of actual data regarding the existence of half bullnoses is not the same thing as actual data regarding a lack of existence of half bulnoses. So, I'll keep looking.
Thanks four your interests in my posts.
(And keep trying to find any half bullnoses, please.)