HP: SAE Gross or Net ?

[Don]

At some point in time, the production car manufacturers converted from SAE-gross HP to SAE-net HP. From the web site:

"My 2003 Z06 has 405 hp and is advertised as one of the most powerful production Corvettes ever produced...yet my brother had a 69 that was rated at 425 horsepower...some models had 450 hp....what's the story? What is the conversion factor from today's horsepower ratings to those of the 60's?"

" The short answer, is that the '69's horsepower was listed in SAE-gross numbers and your ZO6 power is SAE-net, a big difference. This forms the tip of a big, confusing issue that deserves a major explanation. To do that we need to define "horsepower." Unfortunately, how it is defined depends upon who is doing the defining..."

http://neptune.spacebears.com/opine/horsepwr.html

http://www.secondchancegarage.com/public/201.cfm

Questions:

* Year the change was made from Gross to Net ? 1972 is correct ?
* Production car manufacturers, Ford, GM, etc., use the Gross or Net method for their factory crate engines, or ?
* The individual after market engine assemblers, use Gross or Net for their HP ratings, or another method ? Could vary with no consistent approach ?