norms are worthless in the sense that if they didn't stipulate terms up front, they have much less to stand on, but all in all it's pretty common practice for agency's to hold intellectual ownership over their projects. it's just like a normal full-time employee agreement.

it's risky going against them, though. american express has a whole legal team dedicated to finding people who try to show work they did and suing them.

being able to show it in a private setting, like a job interview is different. mainly, they just want to deter people from implying they held the client account and had direct contact and cutting the agency out of the picture.