Only one I could find at OU of that age with either a bio or cv online was Andy Magid, who graduated in 1969 and did a postdoc before taking a tenure-track position there. Seriously, if you have evidence that this was common, provide it.
I think you just showed that such evidence is not likely to be available at a casual Google search. Older professors who probably didn't have to do postdocs are probably less likely to post their CVs online.
