The SCS must record every change to named references, with when it happened, who made it and the new revision identifier, so that the previous states of a branch, how and when they changed and how the current revision relates to earlier ones can be answered. Where revisions have ancestry, the SCS must allow a branch to move only to a descendant of its current revision (in git, a technical control forbidding force pushes). This evidences that the organization intended the changes.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.