With regards to horn nocks they just shouldn't be a requirement, you can use them if you wish..Their should be a separate category for backed and laminate bows as well..Even if using whitewood laminates as they can have  a distinct advantage over  self longbows..
Skeaterbait, look at it this way, if 8/8th's is a square  inch 5/8th's is a cross section which is an inch wide, and 5/8th's of an inch thick.
Rich