I think whats changed is there is no "weighted piston" anymore, no weight given nor diameter of cylinder stated, not weight per square inch remarked. I think they just fluff up an ounce of feathers and put it into a graduated cylinder with no weight and see how much room it takes up AND they do not then compress it down to see whether or not it actually takes up 0NE (1) unit of volume, also done under some un-stated amount of pressure/weight.
It is not obvious that there are in fact any standards or whether the "weighted piston" could be a piece of paper. So the stated fill power whether 700, 800, 850 or 900 has no meaning except price.
The marmot site says "if your down product says it is filled with 800 down, then it is filled with certified 800 fill power down"
Try searching on "down fill certifications" or "certification of down fill" on the Internet. The is NOTHING. You would think that a lab that certified down would be listed huh???
These are my own opinions based on wisdom earned through many wrong decisions. Your mileage may vary.