Thanks. Do you have some schedule, when the documentation will be updated? Or is this a “hobby” project, where everything is done when it fits?
I would it find easier to learn Jupyter development if there is no documentation at all on some topics rather than documentation that refers to an outdated version and does not work. One can still link to the extension examples of older versions just for getting an idea, if one clearly declares those examples as incompatible.
But you can’t link to documentation parts for version 2.0 from the documentation of 3.0 without making clear that this documentation won’t work.