fyi, there's this thing in judging MB's (show & street class) about "authenticity"... for year and model. Authenticity for any item is generally 50% of points (in MBCA sponsored shows). the other 50% are split evenly (25% each) between "condition" and "cleanliness" ... rust, scrapes, abraisions at joints between joined chrome pieces,and chrome swirl marks, ridges, waviness, chrome "patina" (hazyness), overspray ..., etc. are "condition"... dirt, bugs, dust, water-marks, etc. are "cleanliness."
In MBCA judging, however, the team of judges (maybe 2-3 for each of 4 area's of judging a car
-- Exterior Chrome, Trim, Seals, Lights/Signals;
-- Interior;
-- Exterior Body & Paint, Softtop; &
-- Engine ---
-- and added area for Show Class, Chassis / Undercarriage)
only have n minutes to spend on each car in a show, so both level of experience, expertise in a given model & year and time to look for every detail come into play. Sometimes some things will be missed that would otherwise give cause for deduction in points. This (horn hub 1-ring, 2 rings thing) is one of them, to be sure, probably mostly for 1 reason --- expertise of judges in knowledge of a specific model vintage details. For the 230SL's, there's unlikely to be judges that will distinguish between early and late 230SL features, or deduct points for differences between early and late 230SL interchanges... in my opinion.
I've taken a day long MBCA judging school class and have only recent and limited show & street class actual judging experience, but this is my best take given what I've learned and experienced to date.