That reality is that, if a person sees or knows of a public safety hazard or fire risk, they have a responsibility to report it, period. Poorly installed or improperly cleaned kitchen exhaust systems are a fire hazard. All exhaust cleaners use the "risk of fire" as a sales tool to one degree or another.
Cleaners who claim that they didn't know anything, yet are "Certified" are deluding themselves. You can't have one (the claim to be certified) without the other (knowledge of what you are certified to -- #96, PWNA or IKECA Standard). Insurance companies and the court are not going to buy this "Certified ignorance" argument.
So, if you or your crews wish to use ignorance as the reason why you "didn't tell the restaurant that they had a serious problem," with obvious installation problems, access or cleanability of the exhaust system, then I would suggest that you stay as far away from any knowledge that NFPA 96 even exists.
For those of you who are Certified, it is too late. In your case the only hope is education. Maybe "training" your crews (which, as your certified selves know, is what it says in #96) will save you. Otherwise I see no defense for you. In fact, I may see you in court.