The notion of "complete coverage" is fantastically subjective and contextual. The Civil War is, in various scopes, completely covered in several page articles and several volume sets. Word count ranges are a good way to convey expected scope.
Perhaps "complete" is not the right adjective -- something along the lines of "appropriate" might be more fitting. I was driving at "complete" with respect to the purpose of a given assignment.
I think that the article makes a strong case, which meshes with my personal experience as both student and teacher, that word count ranges aren't always a good way to convey the expected scope. If you're a regular contributor to a magazine, with a well-defined and professional style, then a target length can be a reasonable metric. For students in their formative years, such a metric can lead them astray.
