I really feel that the wording about requiring rosters to show the libero number and the "regular" number came from a misguided understanding by NFHS of how liberos would be used. The rules-makers seemed to think that the teams would change liberos quite often during a match, almost with the thought that coaches would give everyone on the team a chance to be the libero. They really didn't comprehend that only one (sometimes two) players would play the libero position. So they figured that the team would need to list both the libero and regular uniform number since they would use three or four or five liberos every match
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I didn't even realize that the rule was still in the book. It's really outdated and ought to be removed.