What about the cutoffs on the transcript (179, 180.5, 182)?
Those are on the transcripts, yes, but they denote the different grade cutoffs for honors at graduation and the percent of each class that historically gets them (e.g. I think Highest Honors is something like 0.4%).
The problem with those honors cut offs as proxies for estimating class rank is just what I said, they are for graduation. Because of that, they account for more classes people have taken over time. Putting aside the changes in available grade medians for classes (things like seminars are not required to stick to 177 median), the addition of transfers and their (usually inflated) grades and changes in behavior, the increased sample size narrows the curve and reduces the standard deviation in a way that is misleading. As a result, the numbers on the transcript will tend to skew the cut offs for a range if it is applied to a class after 1L year. It's highly unlikely that a 180.5 represents the top 3.8% of the 1L class (though not impossible, granted).
So, in short, those numbers aren't perfectly reliable.
EDIT: I also see that the person who asked this has answered questions in Legal Employment, in which case, if they are not an incoming Chicago 1L, I regret spending time answering it and wonder why they are in here asking.