I have no idea where the "10% of solved cases" thing comes from, but I posted across thread: I looked at effectiveness
very carefully in my own muni, and my conclusion was that the cameras were of basically no help. It feels cynical to make this observation, but if I had to bet --- from the way our own PD, which I respect a lot, tried to formulate an argument for keeping the cameras --- they're counting every crime where an involved car blipped an ALPR. That's not at all the same thing as solving a crime.
Someone who knows more about how Flock generates that stat could say more.