Slope is not the same as course rating, the course rating hasn't changed except now instead of a rounded SSS we have an exact to one decimal point CRSince the introduction of Slope in GB&I with WHS, this isn't true.
It also wasn't completely true before 1983.
All else flows from the CR, so it is true, if a course is rated incorrectly then, it still is now, slope is just another layer of fudge to the system