Which really gets back to the fact that grade listings in owner's manuals are a recommendation and not a requirement. Caveat being that if an inappropriate grade damages the engine then that's the user's fault, but no engine is going to be damaged by a higher grade than the recommended one(s). It may be damaged by a lower grade however. MOFT always wins.
People on here like to say that certain grades are "allowed" or that it's a warranty requirement which isn't supported by any statement in the warranty information except what I noted above. Once you know the genesis of the wording in the manuals it makes sense why they say it the way they do. It's not predicated on a technical or mechanical requirement.
