The RBN guidelines allow for differences in authoring style, so long as it's applied consistently and remains fun for the player. So in this manner, you *shouldn't* be able to fail a song just because you hadn't seen it in an HMX track previously. (e.g. sax as vocals)
As such, in borderline cases, it's preferable to post to the PR thread and inquire: "Did you intend to chart it this way?" *Hopefully* the author has noted such decisions in the first post, though, so it's never in question.
Or at least that's how it's *supposed* to go...
Best laid plans, all that rot.