Tags on Air are version-specific. While you aren't currently able to apply the same tags to new versions of a tagged asset or file, you can still leverage the tags used on the previous version!
When you search for content in your workspace using a tag, the result will include the assets and files that have it, even if the tagged content is not the cover version.
Try it out in your own workspace!
Create a stack by adding any file or asset as a version to another asset or file that has different tags or no tags at all
Return to your workspace's all assets & files
Search a tag that is not included in the cover version of the stack you just made
The results will still return the new version because it is associated with the previous version using Air's stack capabilities!
To maintain this searchability:
Keep your stacked assets, stacked
Do not delete versions individually -- deleting the version also deletes its metadata
Closely monitor your user access levels -- make sure the users that have the ability to add and remove content are aware of the importance of your version stacks
Train your team -- help folks who interact with your workspace to know how Air works to help them find what they are looking for.