As I said, it's an interesting question, regardless of the source.
So I went and looked it up, since that seemed more productive than fighting endlessly over it.
The NSF study helpfully includes an appendix that shows what fields they counted as "Computer Science", and it turns out that "Data Processing" and "Data Processing Technician" were indeed counted in that category.
Of course, that says nothing about the relative numbers and how they changed, but it does raise a possible explanation for the shift in numbers as Data Processing died out as a field.
