The key values may change, but those listed above comprise a minimal useful set. If you add unsupported key values to your document, they will be ignored, but you may find them useful as metadata.
However afterwriting (CLI and web) prints all key-values on the title page after the contact block.
The spec says the title page should ignore unrecognized keys, as per https://fountain.io/syntax/#title-page:
However afterwriting (CLI and web) prints all key-values on the title page after the contact block.