If the stuff met a manufacturer?s specifications it would say so on the jug and on the web site of the aftermarket coolant vendor.
Coolants are formulated by chemists and engineers to match the materials in the engines and associated components that contact the coolant. Maybe 30 years ago it used to be a one size fits all vehicles, but not any more. Does your OEM coolant contain phosphates, silicates, nitrites, benzoate, tolyltriazole , Molybdate, or borate? Why does it or does it not? What happens if you replace the coolant with something that does not?
I am willing to bet that in most cases the PG coolants are not certified to meet the manufacturers? requirements not because of the PG. It is because the rest of the formulation does not match.
The take-home message is that if you use coolant that does not meet the auto manufacturer?s specifications and your heater core blows out. You are probably out a few hundred to replace it. If you are post-warranty, you may cause a failure of the heater core, gaskets, water pump, radiator,?. If you use the wrong coolant.
Me, I will use coolant that the corrosion chemists and engineers say is O.K., and dump the more concentrated coolant down the drain as the local authorities suggest. I have tried to find a place to recycle it, with no success. The stuff that is very much diluted by flushing goes off the driveway. It is not practical to try to recover every molecule. I deal with chemical disposal issues all the time; you have to judge relative risks.
A web link to prove something? Assuming that you are not kidding:
Just for fun, Ford TSB Article No. 01-23-6 11/26/01 among other things says, no propylene glycol, and claims of toxicological and environmental advantages of propylene glycol over ethylene glycol may be misleading.
Here are some more links as an introduction to the complexity of coolant chemistry in modern engines (engines and cooling systems are not just iron and copper/lead solder any more). Have fun: