Also, we know that censorship on FR, etc encourages self-censorship, for the usual reasons of shame, fears of legal action, and fears of being called dishonest or a troublemaker.
STOPP collected some fairly decent records but used all kinds of phony excuses to hide the vast bulk of their research from the public. However, they did confirm, in general statements, that CP of teen schoolgirls was very common in certain schools. Needless to say, the teachers behind STOPP were not the teachers spanking the schoolgirls at the time.
In the end, there is no extracting the full truth.
Even if you take a woman who attended such a school as described, her memory will be more than likely a vague “The teacher slippered boys and girls on occasion” even if she got the same punishment sometimes.