Even if the target audience knew what was meant by the tshirt instructions, there’s no reason not to be clear.
We have this issue atmy office actually. There ard apparently people who are overly casual on casual Friday. So they keep sending out these vague clarufucations that don’t clarify. Thus leaves all the rest of us reading and re-reading trying to figure out if it applies to us
At my kids’ high school if they issued a vague insruction like that about jeans and tshirts, you’d have some kids start looking for creative ways of “making choices wisely” that would not be what the administration had in mind.