They don't not bother. They just do it by gut feel without writing anything down about how they're doing it. Admissions counselors at elite high schools "network" with admissions offices at universities to benefit their students in this process. This is common knowledge in the industry to the point that foreign elite high schools, which have a harder time getting name-recognition, spend a pretty sum of money periodically sending their representatives on month-long US trips to go around, say, the top 30 US universities to market their brand.
I took the ACT on a lark my sophomore year of high school. I scored a 29. I also attended one of the top high schools in the nation.
When I was registering for classes in college, my advisor kept trying to put me in Trigonometry or Pre-calculus (I can't remember). Because my ACT score in math said that's what I needed. I took the ACT while I was taking Geometry and Algebra II, so yeah, my math was probably weak. I tried explaining to them that my high school transcript shows I've taken up to Calculus. They wouldn't hear it. I refused to register for any sort of math below Calculus.
Eventually, they told me to go talk to the head of the math department. I told them fine. I went down there all prepared to make my case. As I started to make my case, he saw my transcript, said "Oh, <SCHOOL NAME REDACTED>. What class do you want to take?"
He didn't care about my transcript in the opposite way. I probably could have registered for 300 or 400 level math courses.
