My data is from 2010 when my son was going through the process. It came from the NCAA. The verbiage was something to the effect of 50% of baseball players transfer out to somewhere else (any level) to play before junior year. A 4-2-4 would be two transfers. As you mentioned the 27% probably isn’t the complete picture. It’s too drastic of a change.
“A 2018 study from the National Student Clearinghouse estimates that 39% of all undergraduates who initially enroll in a four-year institution transfer schools at least once.”
Thus would be all sports. I wonder if some sports have higher transfer rates than others.