PCT wasn't invented as much as it just kind of evolved. The people using steroids back when I got involved didn't know much about what they were doing to their endocrine system and really didn't care. They did, as you say, taper up and down and then let the chips fall where they may. Usually in crashes of varying lengths.
The internet was what changed the AS world forever. Boards like this one where medical research could be posted and reviewed brought AS use forward by leaps and bounds. There is no medical school teaching what is common knowledge on these boards. Even doctors like SWILL, I mean SWALE, who make a living on PCT learned most of what they know from the boards.