Yes, that’s true, but in that case you’d have metadata on the other FEP which make it effectively not-FINAL-anymore. Like you have “this version” and “latest version”. I am assuming that any significant update must undergo the entire review process. Once the update becomes FINAL, then a warning on the old one must be shown “This is not the latest FINAL version” or something, similar to what you see at W3C.
If an update is underway in the process, does it have the same title + ID? That might be confusing. Alternatively an update could be part of the same document, i.e. it contains all versions, but that’d be confusing too.
Note that it gets complicated pretty quick. A W3C spec is designed to be something self-contained, whereas a FEP is an enchancement and not necessarily be ‘atomic’ i.e. it may need to be adapted to comply with other FEP’s as they are finalized. There are relationships.
Talking W3C… we may reuse the exact same mechanism. I figure it takes care of most of this. We want the FEP’s to be practical, least ceremonial, but they should also be useful and a sprawl of FEP’s - once the process gets traction - may go against that.
In addition to the FEP process itself arises the question: How to find out what FEP’s an implementation complies to?
I suggest that - for now - this should be in the FEDERATION.md document, proposed last year by @darius in Documenting federation behavior in a semi-standard way? proposed the FEDERATION.md convention, and discussed in SocialCG 2020-02-08.
How this works should be documented in the FEP process too, imho.
Note, I have proposed an extension to FEDERATION.md and will continue discussion in: Improvement to FEDERATION.md convention: Murmurations