Which RFC? The challenge as with all technical specifications is that you have revisions over time and even some times get split up into multiple RFCs. And then as with all interoper issues, is the RFC that you implement the one that other systems you’re interacting with also implementing that RFC. And then even after all of that, you have implementation differences where even if you follow the RFC to the letter, other implementations either made intentional alternate legal choices or had bugs.

RFCs are generally easy to read but there’s a meaningful chasm between understanding the RFC and what actually gets implemented in practice.