Coats are required in competition, that is the first line of the dress code.
I’ve asked you repeatedly whether you are saying that people in your area are wearing polo shirts with no tie with their jackets on (not allowed). You never actually have answered that, but the pictures you posted are of people wearing polos not with jackets or ties. (allowed, when jackets are waived).
Am I inferring wrongly from the photos? Those are NOT what you mean, but in fact you mean riders wear shirts like that with the neck open and a coat on over it? All the time? “Around there”?
Like the look in my first link? Like this?
https://www.google.com/search?q=polo+shirt+with+blazer+on&client=safari&channel=mac_bm&biw=1293&bih=786&source=lnms&tbm=isch&sa=X&ved=0ahUKEwi8zP3V2JnMAhUP5GMKHdxlBZ8Q_AUIBigB#imgrc=24ANJkCS2ztMDM%3A
To the OP: What’s above in the link I showed is not allowed. If you want to wear your coat with NO tie, then, you’ll need to get one of the integrated standup collars you asked about at the beginning.
If you opt to wear a tie of any kind, however, (Bow tie, stock tie, normal necktie, ascot,) then it does not matter what kind of shirt you have on with your jacket and tie. And if jackets are waived due to heat, you must remove the tie, too. But whatever shirt you have on is still fine, as long as it isn’t sleeveless.
You don’t have to go change your shirt to an “approved” integrated standup collar shirt whenever jackets are waived. That’s a misinterpretation that apparently even some judges (?) are making.
People are confusing a kind of shirt, that has been approved as an acceptable replacement for a shirt and tie paired with a jacket, as being the only type of shirt allowed to show in. That isn’t the case.