Why the line on the card gets misread
Paper forces brevity. A printed card has room for three words at most, and three words are not a dress code; they are a guess. Cocktail on a river boat reads differently to a 70th birthday in a hotel dining room, and every guest fills the gap from their own experience, usually at one of the two extremes.
A page has more room, and guests read it on the morning they choose the outfit. A dress code section can be the warm, specific paragraph the card never carried: what the venue feels like, what you would like the room to look like, and what everyone enjoyed wearing last time.