Factory HP ratings -BS or what happened?

Here's some data from Allpar. Most of it is '68, but near the end is a chart of CR and HP for various years. Rated compression remained at 8.4 through most years. The RPM they rated at changed.

http://www.allpar.com/mopar/V6/slant-six-specs.html

I guess it's like most statistics. They can be manipulated. You can usually get the number you want by changing other variables.
So what I'm getting is that the engines of the 70s were nearly the same as the earlier ones. Just that they have been bogged down some by emissions, and they were measuring with a different yardstick...