3GPP 21.900 v20.0.0 — the document's own text
4.9B.4 Considerations for ongoing maintenance, enhancement and new Release versions of specifications
Taught in 3. What a Release is, and what freezing one costs (How standards actually get made, in depth).
When a specific version or all versions in a specific Release of a specification, are withdrawn further versions of the specification in the same Release shall not be created and the specification shall not be promoted to a subsequent Release.
Evolution of specifications and functionality in Releases unaffected by the withdrawal are allowed.
A Category B or Category C CR that adds to or modifies a specification or functionality that has been withdrawn in a subsequent version shall clearly state on the CR cover sheet in the Summary of change that the subsequent version of the specification or functionality has been withdrawn.
Category A CRs for Releases in which the specification or functionality has been withdrawn shall not be produced.