Today, there are three of what I'll call "major" third-party CVE Services clients, Vulnogram, cvelib, and cveClient. Each of these tries to stay up to date with updates to the CVE Record Format, but of course they're also open source and will move at their own pace.
We should, when making updates to the schema, try to coordinate with the maintainers of these clients to let them know about changes, ideally also let them know timelines (this requires coordinating with the AWG about when schema updates will make it into a release), and then offer whatever help we can to get their clients updated to support what's new in the schema.
We should update the RFD documentation to reflect this requirement for future RFDs.