We derive specific keys:

enc_key_attributes = KDF(master_key, "ATTR_V1")
enc_key_documents  = KDF(master_key, "DOCS_V1")
enc_key_metadata   = KDF(master_key, "META_V1")

Each dataset gets its own key.

Rotation = versioning the label (e.g. ATTR_V2 → ATTR_V3).