I have gone through and updated all existing EIPs to match this rule, including EIP-1.
In some cases, people were using markdown citations, I suspect because the long-form was a bit verbose to inline. Since the relative path is quite short, I moved these to inline but I wouldn't be opposed to putting them back to citation format if that is desired by the authors.
In doing the migration/cleanup, I found some EIP references to EIPs that don't actually exist. In these cases I tried to excise the reference from the EIP as best I could.
It is worth noting that the Readme actually already had this rule, it just wasn't expressed properly in EIP-1 and the "Citation Format" section of the readme I think caused people a bit of confusion (when citing externally, you should use the citation format).
* EIP-2364: eth/64: forkid-extended protocol handshake
* EIP-2364: fix review issues from Martin
Co-Authored-By: Martin Holst Swende <martin@swende.se>
* EIP-2364: Add reference to current eth/63 spec
Co-Authored-By: Alex Beregszaszi <alex@rtfs.hu>
* EIP-2364: Fix title to make the web generator happy
Co-Authored-By: Alex Beregszaszi <alex@rtfs.hu>