A ninety-second film cut down to fifteen seconds is not the same film shorter. It is a different argument, usually with a different opening, and it fails when it is produced by trimming rather than by editing.
In generative production the temptation is stronger, because the source material is cheap and a crop costs nothing. What a crop costs is composition: a 16:9 frame cropped to 9:16 loses whichever half of the frame was doing the work.
Plan the cutdowns at brief stage and generate for them. Composing with the vertical crop in mind costs nothing during generation and cannot be recovered afterwards.
Should cutdowns be listed in the brief?
Yes, with their ratios and durations. They are cheaper when they are planned as part of the production and more expensive when they arrive as a request after delivery.
Why not just crop?
Because the subject is rarely in the middle of the frame, and the part that gets cropped away is usually the part carrying the composition. Generating with the crop in mind is free; recovering it is not.