To expand on this answer, current versions of documentation are on-line via a URL that does not have a version in it e.g.
https://4js.com/online_documentation/fjs-fgl-manual-html/?path=fjs-fgl-manual... this is so any links can be persistent across versions. The previous versions documentation is still online and accessible from the documentation page, but it will now have a version in the URL e.g.
https://4js.com/online_documentation/fjs-fglgws-2.41.01-manual-bdl-html/?path=fjs-fglgws-2.41.01-manual-bdlEach time there is a release, the current documentation link is shifted to point to the new documentation and a new link created for the documentation that has just been superceded.
If you think that you will still require access to the older (2 or more prior releases) documentation you should download it onto your servers prior to this occurring.
The same rule of thumb applies to product downloads. You'll note in the downloads area, you can download current and previous versions.