A split skull plate is, well, what it sounds like, a full severing of the bone of the skull, or cranium, thus separating the antlers (or horns). You definitely don't want you or your guide to accidentally do this. B&C won't recognize this because you cannot accurately display/prove the actual inches in spread. The scoring would be rendered unfair if you tried to artificially glue it back together or something, because you would theoretically lose (maybe gain, w/addition of adhesive) length.
Hope this helps!

Kimberly
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Field Staff Writer, WomenHunters