NIST released the SP 800-53 Rev. 5 on September 23rd, 2020.

The Plan of Actions and Milestones (POA&M) is the document that tracks system weaknesses. It's a living document that should be continuously updated throughout the lifecycle of the system.

DoD uses the CNSSI 1253 for security categorization and control selection regardless of whether or not they are true national security systems.

The authoritative source of information for RMF for DoD IT is the RMF Knowledge Service. https://rmfks.osd.mil