Exactly: 'grep -l' can find the list of files with matches in the list of all files, and 'comm -13' can compare that list to the list of all files, so you can find the files missing on the list and...
Often for such tasks 'grep -c ... yourdir/* |sed' is good, where sed can change the counts into na or whatever. Sometimes * makes the command line too long or the arg count too high, your OS may...