The base file chart section in Content Catalog helps to future-proof families when future versions of Revit are used. Many clients choose to manage the oldest version of Revit content they use and let Content Catalog make upgrades available automatically.
Select the name of an item in you results, then select the File History tab when viewing the details of a family.
In the base file chart section shown below, you can see that this family was built originally in 2015 and Content Catalog upgraded it automatically in the cloud for you.
In the photo shown above, here is what each icon represents:
Cloud - the version that Content Catalog automatically pulls from the cloud
"No" symbol - Content Catalog is no longer pulling that version
Paper with arrow - The file version of the uploaded file (also referred to as the "base file")
So, let’s say that your team is using 2020 for a project, in that case, Content Catalog will pull that version from the cloud so that your team doesn’t have to manually upgrade the family. You'll see in the example above that another base file for Revit 2018 was uploaded with changed parameter data. When this happens, Content Catalog will then upgrade the 2018 base file for the latest Revit versions until the next year's uploaded base file (2021 in the above example).
What Content Catalog did here was future-proof this family because now there is a second base file that will be used for future versions of Revit. That means that if any user is using a more recent version of Revit, Content Catalog will use the base file of that version, but will still maintain these legacy versions for projects which are using earlier versions of Revit.
In other words, you don’t have to worry about maintaining multiple versions or multiple Collection for versions of programs.