"Control" of any document, customer's or organization's, DOES entail security of the original document and subsequent revisions. Control DOES imply a procedure for limiting proliferation of uncontrolled copies where the document could fall into hands that could use the document to the detriment of the organization (internally, by building nonconforming product from obsolete drawings; externally, by stealing confidential information.)
The Standards don't address the BMS, they address the QMS. The organization's BMS responsibility is to determine which documents are in the sensitive category where outsiders should not be privy to the information contained. Once determined, appropriate security measures can be applied on individual documents to which they pertain.
My organization's Procedure for protecting against static electricity during assembly is Controlled, is proprietary (because we designed it for our operation), but is not "sensitive," whereas our Procedure for assembling a "black box" is Controlled, is proprietary, and VERY sensitive. We definitely guard the black box procedure and don't allow any "uncontrolled" copies, while we have freely distributed uncontrolled copies of our anti-static procedure to suppliers as a template to set up similar procedures. ("Controlled" copies in our universe are issued to individuals by name, with a "push" mechanism for revisions, collecting the obsolete copies.)