> I assume some tests at least broke that meant they needed to be "fixed up"

OP said:

"However, we did not have any tests asserting the behavior remains consistent due to the ambiguous language in the RFC."

One could guess it's something like -- back when we wrote the tests, years ago, whoever did it missed that this was required, not helped by the fact that the spec proceeded RFC 2119 standardizing the all-caps "MUST" "SHOULD" etc language, which would have helped us translsate specs to tests more completely.