There is a way to publish or share previous versions. See this link for details:
Also, you can fork a specific version, then enable link sharing and post the link here. After that, you can merge your changes upstream.
Note that any previously shared or published version will remain accessible through the version suffix, unless you disabled link sharing or unpublished a notebook at some point (which will make all versions inaccessible).
Lastly, if you want to create a copy without the fork relationship, you can follow the steps outlined in this link: