Question:

Do Document Tags carry over from one Document version to another in Vault?

Answer:

If the current Document version is manually tagged and a new version is created at a later time, the Document Tag carries over to the new Document version.

If Auto-tagging is enabled on a particular Document Tag, then only Document versions with a matching phrase in the Document content are tagged.  This includes any new versions that are uploaded at a later time.  Once the new Document version is uploaded, it is scanned for any phrases that match the automatic tags.  If there are no matching phrases in the new document version, the Document Tag is not added.

Related Documentation:

Vault Document Admin Documentation: Configuring Document Tags