That would mean that all networks which peer with the Internet would necessarily be considered Production. This isn't that reasonable outside certain niches (i.e., national government networks).

Instead, what's commonly done is to provide a Controlled Interface (to borrow a term from those national government networks) that gates which things are at which level of trust. This is where security boundaries are enforced -- and if they are sound security boundaries things on either side can't reasonably damage the other side.