They won't be compatible with each other, guaranteed. Compatibility in reality comes from everyone using the same reference implementations that have been compatibility-tested, not from everyone implementing the same specifications.
I used to do this work in the IETF. take draft specs and write a C implementation and compare notes with the spec authors and other implementations. sometimes I would find a bug later on and see the same bug in multiple vendors implementations, and I would send them mail describing the issue and the fix.
its been very sad for me to see standardization get ignored, and the implementation become the point of reference. for a long time the only way to implement QUIC was to try to extract it from the Chromium code base - a pointless waste of time. but they spec for years was a couple of pages of meeting notes and a sample compression dictionary.
if we continue down this road we are impeding our own ability to evolve. if compatibility is defined by the implementation then were left with nasty balls of antiquated source that we carefully move around and try to plumb into our new environments, but no one really understands.
at the core, things like IP are very straightforward. we can and should specify the semantics of every bit, and have a wide variety of other implementations to test against. this provides a path for us to build new techniques and environments that are still useful in the world that exists today.
