That’s pretty amazing 
I’ve used for the images above freewheels which are newer than that on both of my bikes, but the ones which are mounted are also equipped with this sealing. The only difference is the color; the older ones are black.
(And of course I can’t assure that they are also present on the inside of the freewheels, I’d have to unmount them before.)
These sealings were also the reason why I didn’t let anodize the outer rings, the risk to loose them due to the acid pretreatment was too high.