You don’t question the priorities of the sport already? 
I’d rather either have rules that people actually followed than the current situation, where there’s what’s in the rulebook and then there’s reality and everyone just has to know which rules are actually important.
FWIW (I am probably not on your ground jury!), BN through Modified, I think the shirt above neatly covers both “shirt with choker” (worn with jacket) and “shirt with collar” (worn without a jacket) required by the current eventing dressage dress code:
[LIST=1]
protective headgear—predominantly black or dark blue; Coat—dark color or tweed, tail coats are not permitted; [B]Shirt— of conservative color, with stock and pin, or choker, or tie[/B]; Gloves (if worn)—dark color, tan, beige or white; Jodhpurs, Britches—light color or white; Boots— black, brown, field, jodhpur or a black or brown full grain smooth leather leg piece and matching leather boots. Chaps and/or half-chaps are not allowed. Competitors may compete without a jacket. In such cases, [B]shirt - long or short sleeved with collar and without neckwear, of a conservative color, neatly tucked into riding breeches[/B].
[/LIST]
