I agree with andria93 and cs22 that specifications should be as accurate as you can to make sure all aspects are documented and followed correctly. The limits are an interesting aspect because there are times when there should be upper and lower, or just one, but overall I do think of them as a guideline for validation and testing. In this mini-sim, it was essential to have the COF of a certain degree, thus the guideline was fixed to have a range, through be it small.