I met a Fire Marshall last week that would insist that you had to get it all out the first time!
We cleaned a McDonalds that had a fryer fire, set the suppression system off. It didn't appear to get into the duct, luckily because it hadn't been cleaned in a year and half. The duct was typical McDonalds duct with two elbows making the mid-section inaccessible. We had a hard time getting the top part of the bottom vertical above the hood cleaned. It had a slight tilt back over your head. He insisted that he see no grease in that duct before he would let the store reopen. After an hour of applying chemicals and spraying the same ft' and a half of duct I called him back, he gave the ok, and wants a copy of out paperwork. He looks at it and says this is no good because it says not cleaned to code because of inaccessible areas blah, blah, blah.
I then had to spend the next 30 minutes explaining and showing him that right next to the spot that was so troublesome that he was so anal about is an 8-foot section of duct that has never been cleaned. He just looked befuddled and said he would look into it.