It seems to me that you have found the stated policy and quoted it accurately. If you are searching for a "thou shalt..." in the policy, you won't find it because that's not the way in which policies are stated in polite company. Nonetheless, the absence of those words does not lessen the expectation of conformance with the policy.
There is some confusion today regarding the use of the terms "suggestion" and "recommendation." According to etiquette, a "suggesion" always goes from the "senior" person to the "junior" person and it carries an expectation of conformance (the military explanation is that a "suggestion" should be taken as a direct order) whereas a "recommendation" may go from the "junior" person to the "senior" person and, in any case, leaves discression to conform or not to the judgement of the person to whom the recommendation is given. In a social context, the notion of "seniority" may be established by office or by position of honor as well as by age. Thus, even the use of the phrase "we SUGGEST..." (emphasis added) rather than "we recommend" in this policy statement implies an expectation of conformance.
BTW, the evening's dress always appears in TWO places in the Princess Patter. The first place is on the front, directly below the Princess Patter masthead. The second place is at the top of the evening entertainment section on the third page -- where it's very obvious, if you see it, that it's intended to apply to the evening's entertainment.
As I noted in an earlier post, I'm not clear as to whether the evening's dress is intended to extend to the Horizon Court or not. I have seen this billed as a "casual dining" alternative. I have only gone there after the show and all the passengers seemed to be dressed, but that fact may well reflect only that they had not changed. I suspect that casual attire would prevail there during the early dinner hour.