If you take the pads off and compare the D7200 & D9200 driver they really do look indistinguishable. I took the drivers out of mine to compare and you can really notice a difference when you shine a light through them; The D7200 drive appears to have a crosshatch, woven structure to it, while the D9200's doesn't have this and appears thinner and finer - as Yoshi Fukushima said.According to an interview with Yoshi Fukushima during a visit to the Netherlands (published in Dutch on https://www.alpha-audio.nl/review/review-denon-ah-d9200-over-ear-hoofdtelefoon/ ), the two are distinctly different.. The D9200 driver has a much finer structure. This, combined with an improved suspension mechanism lead to a much faster driver that provides a faster response and a more detailed and refined sound. This was confirmed when using a stroboscope to measure the movement of the driver
Sorry for the poor quality of the pictures - the only way I could take these was with my cheap usb endoscope - but I think you will see what I'm talking about.
This is the D7200 driver:
And this is the D9200:
You can also see a difference if you look at the back of the cone through the vents in the back of the driver.
This is the back of the D7200 cone. From here it actually looks like it has a woven substrate:
This is the back of the D9200 - No woven substrate. The surround also looks different: