Maybe colleges did once-upon-a-time, but in 2017 colleges that do provide yields do so in mid-May, before students are admitted from the waitlist. For example, this from Yale dated May 16, 2017: http://news.yale.edu/2017/05/16/class-2021-one-record-books.
Is Yale going to redo their yield numbers after they take those “pre-qualified” students off the waitlist, and then announce they have a much higher yield? No, as then there would be confusion over calculations and numbers, and Yale would be accused of inflating their yield by admitting too few students and taking those “pre-qualified” ones off the waitlist.