I'm sure you can use on-line search tools to find where and when the term first appeared on the internet. My suspicion is that the phenomenon was being discuss

I'm sure you can use on-line search tools to find where and when the term first appeared on the internet. My suspicion is that the phenomenon was being discussed informally between people who assess students' work, someone used the term "plagiarism", someone will have pointed out that it was "plagiarising" the student's own work, so the prefix was added, and stuck. It's a concept that needs a name, and when a name turns up it often spreads quickly with no obvious source.