I don't know if you thought you were validating or invalidating my argument, but this says exactly what I said.
Further, not only the presense of the words "should" and the doubling down with "recommended", also the absense of the words "must" or "required" or "shall" is pointed.
Because those words are used elsewhere. When something is actually required, those words are used, and so when they are not used, it is meaningful. It means no one is free to put their own words into the authors mouths and say "well they didn't say it but obviously they pretty much meant required" when they so pointedly chose not to say required.
And it's not a technicality. A thing either is or is not required. There are no other states. The spec does not require it, and so for Google to require it, Google is not adhering to the spec.
Since the spec does not require it, you can't say either that it falls under "full implications". "full implications" cannot include "Some servers might require it", because that would be circular logic. No server can require it in the first place.