In Demozoo, we have the concept of the lost tag, which we apply to productions where we have knowledge that a production has existed, but it is currently not available for download anywhere. This helps the community try and find these lost productions, and we frequently find and preserve productions that were previously deemed lost.
Should you be sitting on backups or old cd's or other materials that is tagged lost or is otherwise not preserved on our site, we strongly urge you to upload it to scene.org, or make it available in some other fashion. If you're not familiar with using and ftp client for upload, come talk to us in our Discord, and we'll work something else out to get the files in question preserved for the future.