On 22 Jul 2018, Ken Blake wrote in
alt.windows7.general:

As far as I know NoMoRoBo only catches robo-dialers, so other
kinds of junk calls get through. I haven't counted, but I'd guess
that your 85% is about what I experience with it.

No, the other junk calls that Nomorobo misses are almost all also
robocalls. The trick that gets them past Nomorobo seems to be that they
use fake local numbers and change them very often. Nomorobo's database
is national so if the spammer's campaign is regional and short,
Nomorobo is more likely to miss it.